add markdown killswitch

Markdown interpretation was exposed to XSS attack. It have been fixed, but adding a killswitch that disable the use of markdown could be use-full "in case of".

added Security feature request labels

changed the description

mentioned in commit 3b5a5fa4

mentioned in merge request !237 (merged)

mentioned in commit 539d2bd8

mentioned in commit 28bc47c1

closed with merge request !237 (merged)

closed with commit 539d2bd8

closed with commit 3b5a5fa4

added documentation label

need to write doc about it

reopened

removed Security feature request labels

mentioned in commit e6ce5746

mentioned in merge request !238 (merged)

mentioned in commit 64dab00b

closed with commit e6ce5746

closed with merge request !238 (merged)