Preparation for fixing issue 201

Move tests for gwtp-processors project from gwtp-dispatch-shared to
correct project. Refactor big test into several smaller tests each
testing one specific generator.
Fixing issue #201

If a field has a UseProxy annotation and is of type List or Set, then in
the generated Proxy class this field (and its getters and setters) will
also be of type List or Set.
Extending test case for both scenarios; unfortunately it's not possible
to test if the generic type of the List or Set has been generated
correctly.
Proxies are now correctly generated for all classes implementing either Set or List interface
Adapt tests accordingly.
Merge pull request #280 from bmoritz/master

Fix issue #201: GenProxyProcessor and Lists (Second try)