[TASK] Improve output of EXT:beuser > Permissions > Edit

* Abort link should be rendered as a button
* Preview link was empty
* If no groups are there, don't render the select box
* Add backlink in toolbar

Change-Id: I913bf3ebc2784206afe285ceeb9691231cafcaf9
Resolves: #63122
Releases: master
Reviewed-on: http://review.typo3.org/34429
Reviewed-by: Frank Nägler <typo3@naegler.net>
Tested-by: Frank Nägler <typo3@naegler.net>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>