wiki - editor - enable side-by-side button (#7242)

wiki - editor - enable side-by-side button (#7242)

* wiki - enable side-by-side button in editor

and add some delay so side-by-side live preview is updated
* every 10th keypress
* if keypress < 10 -> apter no input for 1 sec

affects #5436

Signed-off-by: Michael Gnehr <michael@gnehr.de>
* decrease timeinterval user need to stop before rendering is triggered

Signed-off-by: Michael Gnehr <michael@gnehr.de>
* removed not needed code with simpleMDE placeholder

Signed-off-by: Michael Gnehr <michael@gnehr.de>
* run highlight.js on markdown preview

Signed-off-by: Michael Gnehr <michael@gnehr.de>
* fix white border around side-by-side preview

Signed-off-by: Michael Gnehr <michael@gnehr.de>