type verification of the interface for the smart contract

[adridadou]

Right now the checks done are:

• does the function name on the smart contract and the interface match
• does the number of parameters in both functions match

The missing checks are:

• matching return type between the smart contract and the interface
• matching parameter types between the smart contract and the interface

The tricky part here is to check that exists a conversion path between both that makes it compatible or not.