[FEATURE] Allow stripping of empty tags in HtmlParser

Add a stripEmptyTags method to the HtmlParser
It can be enabled by TypoScript or TSConfig:

HTMLparser.stripEmptyTags = 1
HTMLparser.stripEmptyTags.tags = h2, h3
HTMLparser.stripEmptyTags.treatNonBreakingSpaceAsEmpty = 1

Resolves: #20555
Releases: master
Change-Id: I640486e9f32da6ac1eba05e3c38d15a0aba41055
Reviewed-on: http://review.typo3.org/16975


Reviewed-by: Frank Nägler <typo3@naegler.net>
Tested-by: Frank Nägler <typo3@naegler.net>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>