Fix minor bug with staff feed source

If for some reason a staff does *not* have roles for the school he belongs
to theb an exception will be thrown when rendering the staff_feed_source.

This shouln't happen under normal circumstances but the behavior has been
changed to just output an empty role instead of throwing the exception.
Merge remote-tracking branch 'upstream/develop'...

into origin/develop.

Conflicts:
	django-verdant/rca/models.py
Merge remote-tracking branch 'spapas/develop' into staging