[BUGFIX] Don't use modulemenu classes in topbar

When the startModule setting is empty a strange behaviour
takes place. This happens because the module menu classes are
in use in the topbar too.

Fix this by adding a specific t3js-mainmodule class.

Resolves: #66893
Releases: master
Change-Id: I46768c1f81a2616bd279eacfa5b2e38c863b582e
Reviewed-on: http://review.typo3.org/39461


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>