Merge branch 'cleanup_backend' into 'django3_migration'

beat/web/backend/__init__.py

beat/web/backend/admin.py

beat/web/backend/api.py

beat/web/backend/apps.py

beat/web/backend/helpers.py

beat/web/backend/local_scheduler.py

beat/web/backend/management/commands/cleanup_cache.py

beat/web/backend/management/commands/qsetup.py

beat/web/backend/migrations/0001_initial.py

beat/web/backend/migrations/0002_scheduler_addons.py

beat/web/backend/migrations/0003_remove_result_syserr.py

beat/web/backend/migrations/0004_environmentlanguage.py

beat/web/backend/migrations/0005_job_modifications.py

beat/web/backend/migrations/0006_localschedulerprocesses.py

beat/web/backend/models/__init__.py

beat/web/backend/models/environment.py

beat/web/backend/models/job.py

beat/web/backend/models/local_scheduler.py

beat/web/backend/models/queue.py

beat/web/backend/models/result.py