Detector for invalid using for at the top level

[bart1e]

This PR implements the detector for the incorrect usage of the using-for statement: in Solidity it is possible to write using <library> for <type> even when <library> does not contain any function that has <type> as its first argument. Such a code will compile even though the statement has no effect.

This detector detects such incorrect usages of using-for statements, currently only for top level using-for statements (#1652 has to be solved in order to implement detector for contract level using-for statements).

It contains several utility functions checking if a certain type may be implicitly convertible to some other one - we can consider moving them to relevant classes (for instance these related to ElementaryType may be added there).

There is one issue though - I wasn't able to get information about the address type: if it's payable or not ("normal" address is not implicitly convertible to address payable, but I am unable to impose this rule right now). Detector now always says that address types are implicitly convertible to each others - it won't bring any false positives, but we may get some false negatives.

[montyly]

This is great work, thanks @bart1e