Support "duplicated" type definitions

[K-Phoen]

This PR is an attempt at solving #666

The approach taken here is heavily inspired by #667, of course updated to work against the next branch.

From a high level, the following changes were introduced

• when duplicated definitions are identified, we lift the ambiguity by generating new names for the definitions. This is done in the SchemaGenerator and mainly by the unambiguousName() function
• since we need relevant information to generate decent new names, some parser components were extended to give us access to the file name from which definitions originate. For conflicting definitions, the non-common parts of the file names are used as "disambiguated names"

Storing the file name for relevant types is done in the first commit, the second one does the duplicate definitions detection + disambiguation.

[K-Phoen]

The only actual work performed by this function is here, in the next 3 lines.

Everything else is just recursively traversing the schema.

[domoritz]

I think I am hesitant to accept the added complexity (regexes etc) right now. If you can find a simpler solution, I would be happy to consider it, though. I'll close this for now since the base has moved too much to merge this anyway.