[!!!][TASK] RTE reloaded

Main refactoring of RTE on PHP side. Classes AbstractRte,
RteHtmlAreaBase and the instantiator API RTEgetObj() are
dropped and inlined to the FormEngine class construct.
Lots of code is simplified or moved around.

Change-Id: Ibd4ff3e7fa8fe695a96b03355c905640d2efa351
Resolves: #67917
Releases: master
Reviewed-on: http://review.typo3.org/40842


Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>