[test] drop dependency on third party cubes
Drop dependency on cubicweb-file, cubicweb-localperms, cubicweb-tag and
cubicweb-comment for cubicweb.test and cubicweb.sobjects.test
Move cubicweb/test/data/libpython/cubicweb_* to cubicweb/test/data, so it's
included in PYTHONPATH.
Add missing parts of schema, entities, views, hooks that make tests pass.