[TASK] EXT:form - make 'grid rows' independent from 'grid containers'

* Create 'grid rows' without 'grid container' wrappers
* Disable 'grid containers' within the form editor by default
  because twitter bootstrap prohibits container nesting

Resolves: #80455
Releases: master
Change-Id: I3997943858ac3b235094b765697f724cb1e4c95d
Reviewed-on: https://review.typo3.org/52166


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>