As part of AA-500, we added a completeness check to showing the
banner since we didn't before. As part of AA-260, we now take into
account if a learner has more attempts left on a problem (regardless
of completeness) and allow them to shift their dates to try again.
* Moving plugins infrastructure to edx-django-utils
This PR extracts the code that enables plugins in edx-platform and puts it in edx-django-utils. This is done to allow other IDAS to add plugin functionality.
This also has an initial use case for Personalized Learner Schedules
to add CTAs to capa and vertical blocks to allow users to shift their
course deadlines.
