[TASK] Setting space before/after should use !important

If the setting space before/after is used, the generated styles
should use !important to override possible CSS styles done somewhere else.

Change-Id: Ib2cbef280e6d2ac9d1503448ebaede48cf9d159b
Resolves: #50038
Releases: 6.2,6.1,6.0
Reviewed-on: https://review.typo3.org/22356
Reviewed-by: Markus Klein
Tested-by: Markus Klein