Add a "Send Test Notification" button to make testing the server easier
Summary: Ref T4324. Currently, it's a bit of a pain to send yourself notifications, and often involves multiple browsers. Instead, add a button to send them.
Test Plan: {F114495}
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T4324
Differential Revision: https://secure.phabricator.com/D8255