* Deadlock detection: the chatbot handlers will spin off a background goroutine
to ping DMs at itself and test for responsiveness. If the echoes don't return
for a minute, issue a /api/shutdown command to the HTTP server to force a
reboot.
* New admin API endpoint: /api/shutdown, equivalent to the operator '/shutdown'
command sent in chat. Requires your AdminAPIKey to call it. Used by the chatbot
as part of deadlock detection.
* Adjust some uses of mutexes to hopefully mitigate deadlocks a bit.
* Do Not Disturb: if users opt to "Ignore unsolicited DMs" they will set a DND
status on the server which will grey-out their DM icon for other chatters.
* Bring back an option for ChatServer to notify you when somebody begins watching
your camera (on by default).
* Automatically focus the message entry box when changing channels.
* Lower webcam resolution hints to 480p to test performance implications.
