[TASK] Introduce new "Important" type of documentation

Resolves: #67159
Releases: master
Change-Id: Ia17a3a52914b7acaab47b0d1bb84395a7d3fa917
Reviewed-on: http://review.typo3.org/39760


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>