Converted all status icons to be managed by scss colors only and deleted any classes or styles within the svg's, plus gave status badges a hover style only if clickable

This commit alters views for the following models to use the markdown cache if
present:

* AbuseReport
* Appearance
* ApplicationSetting
* BroadcastMessage
* Group
* Issue
* Label
* MergeRequest
* Milestone
* Project

At the same time, calls to `escape_once` have been moved into the `single_line`
Banzai pipeline, so they can't be missed out by accident and the work is done
at save, rather than render, time.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6084#note_15026132

Closes #19804

cumulative builds time. Closes #17007

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb