CORE-6267 UI no longer gens ID for selection items

* After saving a new app, or an existing app which contains new sections
  or arguments, the UI will update its bound model with the generated
  IDs returned from the app save endpoint.
* The UI no longer generates IDs for new SelectionItems. This includes
  the hierarchical list selector and all other basic selectors. New
  items are submitted without IDs, and are updated with the IDs provided
  by the save/update endpoints.
* All ListStore<SelectionItem> are now instantiated with
  SelectionItemModelKeyProvider. This new provider uses keys which are
  stored in the autoBean's tags. This is keyed by the
  SelectionItem.TMP_ID_TAG constant. Look at
  AppTemplateUtils.addSelectionItemAutoBeantIdTag(..) to see how these
  ids are set on the autobean.
* Updated the signatures of AppTemplate saving, publishing, and
  updating methods to return AppTemplates instead of Strings. Each of
  these methods now uses the AppTemplateCallbackConverter.
* AppTemplate callback converter has been updated to apply IDs generated
  for new SelectionItems to the AutoBean tag mentioned above.
CORE-6267 Cleanup of classes from previous commit
CORE-6267 Removed ignored and erroneous test