We need to keep the email lookup as we want to fall back to displaying
the gravatar result for a given email if the user does not exist.

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.

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

This ensures all these calls have an author set, allowing the use of
"all" mentions where possible.

Make the following changes to deal with new behavior in Rails 4.1.2:

* Use nested resources to avoid slashes in arguments to path helpers.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Didn't bother with files in db/, config/, or features/

Project - restyled show page, removed info page
Repository - restyled show page, added download option
Tags - added download options