Updated playlist management API

api/config/api_urls.py

api/funkwhale_api/playlists/models.py

api/funkwhale_api/playlists/serializers.py

api/funkwhale_api/playlists/views.py

api/tests/playlists/test_serializers.py

api/tests/playlists/test_views.py

api/tests/users/oauth/test_api_permissions.py

docs/swagger.yml

front/src/components/playlists/Editor.vue

front/src/components/playlists/PlaylistModal.vue