Add Aave Leverage Module (#116)

* Add aave V2 token interfaces

* Add Aave Leverage Module contract

* Add tests for module contract

* Remove unused parts of interfaces

* Add suggested changes

* Add ReserveTokens struct
* Emit events on lendingPool and aave reserve update
* Optimize removeStorage calls

* Add tests for deleverToZeroBorrowBalance

* Avoid explicitly invoking setUserUserReserveAsCollateral in lever()

* At first issuance when user transfers aTokens to SetToken via the
issuance module, Aave enables that asset to be used as collateral by the
SetToken

* Remove ability to take stable debt

* Stable debt is not required in structured products on mainnet
* stable debt is not supported on Matic

* Increase test coverage and fix bugs

* Add tests for setTotalSupply == 0 in sync and remove checks for
usageAsCollateralEnabled

* Add tests for assets initialized but not part of Set position

* Refactor validateNewCollateralAsset and validateNewBorrowAsset

* Add javadoc comments for internal functions

* Rename addAaveReserve to updateUnderlyingToReserveTokensMapping

* More verbose naming
* Added return param docs to internal functions

* Add integration tests written by @richardliang

* Format comments to natspec specification

* Attempt at fixing coverage, removed WETH borrow

* Fix addCollateralAsets, removeCollateralAssets and removeModule
functions

* Make sure the fuctions do what the manager expects them to do
* Maintain state consistency between aave and ALM

* Refactor tests to include above changes

* fix test comments

* Skip integration tests

Author: 0xSachinK

contracts/interfaces/external/aave-v2/IAToken.sol

@@ -0,0 +1,21 @@
+/*
+  Copyright 2021 Set Labs Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache License, Version 2.0
+*/
+pragma solidity 0.6.10;
+
+import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+interface IAToken is IERC20 {}

contracts/interfaces/external/aave-v2/ILendingPool.sol

@@ -1,4 +1,20 @@
-// SPDX-License-Identifier: agpl-3.0
+/*
+  Copyright 2021 Set Labs Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache License, Version 2.0
+*/
 pragma solidity 0.6.10;
 pragma experimental ABIEncoderV2;
 

contracts/interfaces/external/aave-v2/ILendingPoolAddressesProvider.sol

@@ -1,4 +1,20 @@
-// SPDX-License-Identifier: agpl-3.0
+/*
+  Copyright 2021 Set Labs Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache License, Version 2.0
+*/
 pragma solidity 0.6.10;
 
 /**

contracts/interfaces/external/aave-v2/IProtocolDataProvider.sol

@@ -1,8 +1,24 @@
-// SPDX-License-Identifier: agpl-3.0
+/*
+  Copyright 2021 Set Labs Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache License, Version 2.0
+*/
 pragma solidity 0.6.10;
 pragma experimental ABIEncoderV2;
 
-import {ILendingPoolAddressesProvider} from "./ILendingPoolAddressesProvider.sol";
+import { ILendingPoolAddressesProvider } from "./ILendingPoolAddressesProvider.sol";
 
 interface IProtocolDataProvider {
   struct TokenData {

contracts/interfaces/external/aave-v2/IStableDebtToken.sol

@@ -0,0 +1,28 @@
+/*
+  Copyright 2021 Set Labs Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache License, Version 2.0
+*/
+pragma solidity 0.6.10;
+
+import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+
+/**
+ * @title IStableDebtToken
+ * @notice Defines the interface for the stable debt token
+ * @author Aave
+ **/
+
+interface IStableDebtToken is IERC20 {}

contracts/interfaces/external/aave-v2/IVariableDebtToken.sol

@@ -0,0 +1,27 @@
+/*
+  Copyright 2021 Set Labs Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache License, Version 2.0
+*/
+pragma solidity 0.6.10;
+
+import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+
+/**
+ * @title IVariableDebtToken
+ * @author Aave
+ * @notice Defines the basic interface for a variable debt token.
+ **/
+interface IVariableDebtToken is IERC20 {}

contracts/interfaces/external/aave-v2/lib/DataTypes.sol

@@ -1,4 +1,20 @@
-// SPDX-License-Identifier: agpl-3.0
+/*
+  Copyright 2021 Set Labs Inc.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache License, Version 2.0
+*/
 pragma solidity 0.6.10;
 
 library DataTypes {