PLF-5728: Use custom data validator for Navigation Node's Name

Fix description:
* Use custom identifier validator for Page Node Form. The validator is defined as system properties.
PLF-5648: Unknown Error when cutting a node into its child.

Fix description:
* Forbid to move a node into its child.
PLF-5514: [Space Navigation] Show more button still appears when there are no more results

Fix description:
* Hide "Show more" button during searching space.