[TASK] Hide msg "Show hidden content elements" if none are hidden

To improve the usability the message and checkbox should only be
shown if there are elements actually hidden.

Change-Id: I0bb652ce915d1e8896b38bf3f94ae2a276cc3881
Resolves: #68037
Releases: master
Reviewed-on: http://review.typo3.org/41081


Reviewed-by: David Greiner <hallo@davidgreiner.de>
Tested-by: David Greiner <hallo@davidgreiner.de>
Reviewed-by: Frederic Gaus <frederic.gaus@flagbit.de>
Tested-by: Frederic Gaus <frederic.gaus@flagbit.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>