Use format() instead of %
Remove unused test files
Test VerbNetFrameSet.mark_as_removed/shown()
Link to searched classes

This patch uses select_related so that the number of queries stays
constant.
Restore get_all_members... as a non-static method
Guess related_name in get_all_verbs

Before that, the function was named
get_all_members_or_manual_translations and we had to pass the
related_name. To avoid mistakes and to improve the code, we now pass
VerbModule (VerbTranslation or VerbNetMember) and guess the
related_name.
Stop modifying verbs in a get_ function

The resulting side effect could have been surprising.
Move verbs instead of removing/adding on update
Allow to move verbs between subclasses
Add settings for a 'migrated test DB'

The idea is not to have to create a new DB and apply our costly
migrations for each test.
Remember the original subclass when sending verbs