Sal 4.1.3

Changes

• Fix broken OS plugin.
• Reduce queryset filtering to once from twice (or maybe thrice) for machine datatable list views.
• Fixes #382 (KeyError for "unknown" management sources).
• Fix plugins which were setting datetime.datetime.now() once, globally being more and more off the longer Sal is up.
• Update Django, DRF, gunicorn, etc.
• Migrate DRF schema generation to current, explicit method.