refactor: apply structure to favorites and saveable things

src/core/things/Favorite.ts

@@ -12,7 +12,7 @@
  * You should have received a copy of the GNU General Public License along with
  * this program. If not, see <https://www.gnu.org/licenses/>.
  */
-import {SCSaveableThing} from '../base/SaveableThing';
+import {SCSaveableThing, SCSaveableThingWithoutReferences} from '../base/SaveableThing';
 import {SCThingMeta, SCThingType} from '../Thing';
 import {SCAcademicEventWithoutReferences} from './AcademicEvent';
 import {SCArticleWithoutReferences} from './Article';
@@ -37,6 +37,13 @@ export type SCFavoriteDataTypes = SCAcademicEventWithoutReferences
   | SCSportCourseWithoutReferences
   | SCToDoWithoutReferences;
 
+/**
+ * A favorite without references
+ */
+export interface SCFavoriteWithoutReferences extends SCSaveableThingWithoutReferences {
+
+}
+
 /**
  * A favorite
  *