refactor: use enumeration for the type of an origin

src/core/things/Favorite.ts

@@ -41,6 +41,9 @@ export type SCFavoriteDataTypes = SCAcademicEventWithoutReferences
  * @validatable
  */
 export interface SCFavorite extends SCSaveableThing<SCFavoriteDataTypes> {
+  /**
+   * Type of a favorite
+   */
   type: SCThingType.Favorite;
 }