trix_core.multiassignment_serialize: Rename coursetag to course_tag.

Matches the naming in models.py.
trix_core.models: Normalize newlines and tabs in assignment clean().
project.default.settings: Set login and logout url settings.
project.develop: Updated test data to use \n for examples.
trix_core.multiassignment_serialize: Dump with allow_unicode.
Working multiselect editing, but there is something wrong with the

validation.