Adds separator style to toolbar items. Also the positioning of fly-out menus is
reworked and does not rely on JavaScript anymore.

Change-Id: Ie3b1dab2af211ad161703fcf92b10bd9ec889acc
Fixes: #32450
Releases: 4.7
Reviewed-on: http://review.typo3.org/8987
Reviewed-by: Tolleiv Nietsch
Tested-by: Tolleiv Nietsch
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter