Merge part of stable/1.5.x into master.

Conflicts:
	openslides/agenda/views.py
	openslides/mediafile/forms.py
	openslides/projector/api.py

The fix from commit 39de1924cb9dcfa93a5bdd95fa30c273f72fe420 was removed
because of the new widget system in master branch. See GitHub Issue #1191