Bug #5, modify "Add Stumbling Block" widget - edit Student Problem UI

* Mods to "admin" JS/Javascript, Custom-Post-Type base class, CSS ...
* Hooks into existing auto-complete/ suggestions JS behaviour
* Legacy behaviour via "tags-ui" param: /post-new.php?post_type=..&tags-ui=wp
* https://github.com/mhawksey/wp-juxtalearn-hub/issues/5
Merge branch 'master' of https://github.com/IET-OU/wp-juxtalearn-hub into edit-post/CR5/add-stumbling-block