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.
- Some views had a "Close" button. We've removed this, because we don't
want users accidentally hiding the validation errors and not knowing
what needs to be fixed.
- Some views used `li`, some used `p`, some used `span`. We've
standardized on `li`.
- Some views only showed the first error. We've standardized on showing
all of them.
- Some views added an `#error_explanation` div, which we've made
standard.
