[TASK] reStructuredText + YAML syntax highlighting

Replace Ace Editor (http://ace.ajax.org/) by CodeMirror (http://codemirror.net/)
since there is still no support for reStructuredText in Ace Editor.

Resolves: #51841
Change-Id: Ie30dd3b476fc2a159629a163b1a1931e51b19368
Reviewed-on: https://review.typo3.org/26624
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers