Refactor tests: reduce testing layer complexity, eliminate mock tests

:construction: 
I've refactored most tests in order to make them simpler and more robust.

- Drop package builder in favor of `ftw.builder`'s new package builders (4teamwork/ftw.builder#37)
- Replace most bad mock tests with real tests
- Remove all the test GS profiles and upgrade steps; using package builder instead
- Move console script testing layer to `ftw.testing` (4teamwork/ftw.testing#14)
- Clean up testing layers in general

Sorry for the large diff :wink: 
:construction: https://github.com/4teamwork/ftw.builder/pull/37