[BUGFIX] Prevent cut off font icons on zoom

Font icons were cut off on top when browser is zoomed
or subpixel placement is not ideal.

Also corrected the wrong placed CSS classes in the
extension manager on extension import.

Releases: master
Resolves: #65212
Change-Id: If073b9a65550caaa816e68adde3c7758dd9586e3
Reviewed-on: http://review.typo3.org/37070


Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>