Allow to dynamically create elements with purely numeric names in a selector type

Before this was not possible, as this was messed up with the DB ids. Now we prefix the new created values with a special prefix, to mark them as new.

This fixes issue #381

assets/controllers/elements/structural_entity_select_controller.js

@@ -43,7 +43,6 @@ export default class extends Controller {
             selectOnTab: true,
             maxOptions: null,
             create: allowAdd ? this.createItem.bind(this) : false,
-            createFilter: /\D/, //Must contain a non-digit character, otherwise they would be recognized as DB ID
 
             searchField: [
                 {field: "text", weight : 2},
@@ -72,7 +71,8 @@ export default class extends Controller {
 
     createItem(input, callback) {
         callback({
-            value: input,
+            //$%$ is a special value prefix, that is used to identify items, that are not yet in the DB
+            value: '$%$' + input,
             text: input,
             not_in_db_yet: true,
         });