Improve identifier path support

[montyly]

The parsing was failing due to the new IdentifierPath in case of modifier: the modifier name needs to be used instead of its signature

[0xalpharush]

I think this can be fixed more simply by adding all modifier names to the dictionary in addition to their signatures, e.g.

modifiers = {m.full_name:  m for m in contract.modifiers if not m.is_shadowed}
modifiers |= {m.name:  m for m in contract.modifiers if not m.is_shadowed}

I guess there's a potential for clashes?