[#71535126] Remove images and headings from marked

Modify marked to remove images and headings from its parser.
Escape text being shown in comments.
Merge branch 'master' into custom_markdown

Conflicts:
	app/assets/javascripts/kiwi/components/comments/comments.js.coffee
[#71535126] Upgrade underscore, 1.6.0

Upgrade underscore to version 1.6.0
Merge pull request #140 from Forekasting/custom_markdown

Custom markdown