[BUGFIX] Hidden input element in form wizard almost invisible

Hidden input elements in the form wizard are not visualized at
all in the user interface. A dotted border is added to be able
to spot in the wizard.

Change-Id: Ic5d4f12427ba28cf56b4ee609b374aabb2c468b4
Fixes: #28620
Reviewed-on: http://review.typo3.org/6201
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers