Modularize external interface routine

[tonivv]

So far, there are two external interfaces in the leverage tool:

1. Uniswap (FlashSwap)
2. Compound
   Code to interface with these two external smart contracts are intertwined, it would be cleaner and more secure to modularize these interface routines. For example, in contracts/FlashSwapCompoundHandler.sol, functions that are not related to FlashSwap should be moved outside this smart contract. There needs to be a mechanism to call external contracts, changing line 62 from:
   DSProxyInterface(dsProxy).execute(address(this), openLoanLogicData);
   to:
   DSProxyInterface(dsProxy).execute(ProxyAddress, openLoanLogicData); where ProxyAddress here is where Compound interfacing routine, or other routine lives.