[BUGFIX] Use correct active CSS class in RTE toolbars

The button class "active" is used now and replaces the broken
class "btn-active".

Resolves: #67938
Releases: master
Change-Id: I55c0f573c5dbf894e9a82e76a0d345fef1696e2d
Reviewed-on: http://review.typo3.org/40946


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>