Scan outputs of Skycoin wallets

**Is your feature request related to a problem? Please describe.**
Skycoin wallets do not implement `ScanOutputs` method.

**Describe the solution you'd like**
Use Skycoin node's address => outputs endpoint .

- [ ] Scan `LocalWallet`'s outputs
- [ ] Scan `RemoteWallet`'s outputs

**Additional context**
`ScanOutputs` added in `BlockchainVisor` as part of #230 .
