[TASK] Better styling of import table in Extension Manager

Change-Id: I99ba696283f207355142776afa308c09b08b825a
Resolves: #63802
Reviewed-on: http://review.typo3.org/35344
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>