[TASK] ToolbarItem interface improvements

Change new interface splitting item and drop down.
Refactor all toolbar items accordingly.
Styling changes will be done with second patch.

Change-Id: I6bfa87dbc85eb0312f4748283de788e27dda590e
Resolves: #62997
Releases: master
Reviewed-on: http://review.typo3.org/34205


Reviewed-by: Felix Kopp <felix-source@phorax.com>
Tested-by: Felix Kopp <felix-source@phorax.com>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>