Moved actor domain to a dedicated table

api/config/settings/common.py

api/funkwhale_api/federation/admin.py

api/funkwhale_api/federation/factories.py

...hale_api/federation/migrations/0013_auto_20181226_1935.py

...hale_api/federation/migrations/0014_auto_20181205_0958.py

...kwhale_api/federation/migrations/0015_populate_domains.py

api/funkwhale_api/federation/models.py

api/funkwhale_api/federation/serializers.py

api/funkwhale_api/users/models.py

api/tests/conftest.py

api/tests/federation/test_migrations.py

api/tests/federation/test_models.py

api/tests/federation/test_serializers.py

api/tests/users/test_models.py