PerpV2 manager extension internal audit fixes (#10)

* Fix: _calculateCurrentLeverageRatio

* Fix failing tests

* Replace all .mul(-1) with .neg()

* Fix _trade javadocs

* Fix rebalance() javadoc

* Remove .only() from tests

* Fix ripcord() javadocs

* Fix: engage treats dust amounts as zero

* Add functions to IAccountBalance interface

* Add TWAP cooldown period in disengage

* Add warning to to disengage javadoc

* Fix PreciseUnitMath tests

* Engage: Check base position unit instead of balance

* Remove PreciseUnitMath lib and import from setprotocol package instead

* Update setprotocol dependency to 0.11.0

* Fix compile bugs

* Update yarn.lock file

* Fix yarn.lock

Author: Sachin

contracts/extensions/FeeSplitExtension.sol

@@ -22,12 +22,13 @@ pragma experimental ABIEncoderV2;
 import { Address } from "@openzeppelin/contracts/utils/Address.sol";
 import { SafeMath } from "@openzeppelin/contracts/math/SafeMath.sol";
 
+import { PreciseUnitMath } from "@setprotocol/set-protocol-v2/contracts/lib/PreciseUnitMath.sol";
+
 import { BaseExtension } from "../lib/BaseExtension.sol";
 import { IIssuanceModule } from "../interfaces/IIssuanceModule.sol";
 import { IBaseManager } from "../interfaces/IBaseManager.sol";
 import { ISetToken } from "../interfaces/ISetToken.sol";
 import { IStreamingFeeModule } from "../interfaces/IStreamingFeeModule.sol";
-import { PreciseUnitMath } from "../lib/PreciseUnitMath.sol";
 import { TimeLockUpgrade } from "../lib/TimeLockUpgrade.sol";
 
 

contracts/extensions/PerpV2LeverageStrategyExtension.sol

@@ -27,6 +27,8 @@ interface IAccountBalance {
     function getTotalDebtValue(address trader) external view returns (uint256);
     function getPnlAndPendingFee(address trader) external view returns (int256,int256,uint256);
     function getBase(address trader, address baseToken) external view returns (int256);
+    function getTakerPositionSize(address trader, address baseToken) external view returns (int256 takerPositionSize);
+    function getTakerOpenNotional(address trader, address baseToken) external view returns (int256 openNotional);
     function getQuote(address trader, address baseToken) external view returns (int256);
     function getNetQuoteBalanceAndPendingFee(address trader) external view returns (int256, uint256);
     function getPositionSize(address trader, address baseToken) external view returns (int256);