Added sources. Stand 2019-01-24.

backend/en/basis.json

@@ -102,6 +102,7 @@
         "newspapers_mailing_lists": "Newspapers and mailing lists",
         "room": "Room",
         "image": "Image",
-        "menu_items": "Menu Items"
+        "menu_items": "Menu Items",
+        "backgrounds": "Backgrounds"
     }
 }