DEV: select-kit 2 (#7998)

This new iteration of select-kit focuses on following best principales and disallowing mutations inside select-kit components. A best effort has been made to avoid breaking changes, however if you content was a flat array, eg: ["foo", "bar"] You will need to set valueProperty=null and nameProperty=null on the component.

Also almost every component should have an `onChange` handler now to decide what to do with the updated data. **select-kit will not mutate your data by itself anymore**

app/assets/javascripts/admin/controllers/admin-user-index.js.es6

@@ -278,7 +278,7 @@ export default Controller.extend(CanCheckEmails, {
     },
 
     resetCustomGroups() {
-      this.set("customGroupIdsBuffer", null);
+      this.set("customGroupIdsBuffer", this.model.customGroups.mapBy("id"));
     },
 
     savePrimaryGroup() {