User SafeERC20 for ERC20 operations

[alonmuroch]

@adamzigdon @vadiminc @lior-blox

[adamzigdon]

@alonmuroch SafeERC20 is a library that should help you safely interact with foreign tokens that don't necessarily implement ERC20 correctly.
Uniswap had a problem with the BNB token on Ethereum because its transfer method didn't return a value as expected in the standard (for some reason transferFrom did).
The library encapsulates the function call and assumes that the transaction was successful if it neither returned false nor reverted, allowing the methods to lack a return value.