[BUGFIX] Enable class/data-* attributes in RTE elements

CKEditor should allow data attributes and class attribute by
default, otherwise any link added in the typolink popup
will get removed automatically by CKEditor's Content filter.

Releases: master
Resolves: #80666
Change-Id: Ia2bc0308fbe01d96019666010aed036532f8a10d
Reviewed-on: https://review.typo3.org/52349


Reviewed-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>