Improve Aphlict server

Summary:

• Move to port 22280 by default.
• Warn when running as non-root.
• Allow subscription and publish/admin ports to be configured.
• Allow server to drop root after binding to 843.
• Allow log path to be configured.
• Add /status/ admin URI which shows server status.
• Return HTTP 400 Bad Request for other requests, instead of hanging.
• Minor formatting cleanup.

Test Plan:
Ran without root:

$ node aphlict_server.js

...got a good error message. Ran with --user:

$ sudo node aphlict_server.js --user=epriestley

...verified server dropped permissions. Ran with --port / --admin. Hit /status/ with GET, got status. Hit other URLs with GET, got 400.

Reviewers: allenjohnashton, ddfisher, keebuhm

Reviewed By: ddfisher

CC: aran

Differential Revision: https://secure.phabricator.com/D2737