Add a server status page for notification server

Summary:

• Add a /notification/status/ page which shows server status.
• Remove various test controllers and routes.
• Make the "no notifications" message look better.
• Move port/URI configuration to config file.

Test Plan: Started server, hit /notification/status/, saw server status.

Reviewers: allenjohnashton, ddfisher, keebuhm, jungejason

Reviewed By: jungejason

CC: aran

Maniphest Tasks: T944

Differential Revision: https://secure.phabricator.com/D2756