Improve debug support for notifications

Summary: Add a notification.debug setting that shows debug info in the browser. Also improve some logging/error handling stuff and fix a bug with host names.

Test Plan: {F13098}

Reviewers: jungejason, btrahan, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T944

Differential Revision: https://secure.phabricator.com/D2810