[BUGFIX] Gap between module menu items causes collapse on click

Transform the margins between entries in the module menu into paddings
to avoid that clicks on this margin cause collapsing of the menu
section.

Change-Id: Id2b75826c91f84904b52567a5e31e240288018fd
Resolves: #27634
Releases: 4.6, 4.5
Reviewed-on: http://review.typo3.org/2925
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert
Reviewed-by: Kay Strobach
Tested-by: Kay Strobach
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Susanne Moog
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Tested-by: Georg Ringer
Reviewed-by: Georg Ringer
Reviewed-by: Andreas Wolf
Tested-by: Andreas Wolf