R1:79366795e7ad

React to Aphlict disconnects in the UI

Summary: Ref T5365. Surface disconnects in the UI.

Test Plan:
- Connected, then killed the server.
- Saw disconnected event and appropriate update in the UI.

{F169605}

Reviewers: joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T5365

Differential Revision: https://secure.phabricator.com/D9706