[FEATURE] EXT:form - support multiple form elements per row

Make it possible to define multiple form elements per row.
The default configuration works for Twitter Bootstrap.

Resolves: #80196
Releases: master
Change-Id: I28b9f648d2bc202c03b6c6b474f6e975ef1459bd
Reviewed-on: https://review.typo3.org/52037


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>