Rig up chat to be suitable for a Doge election. (Hopefully.) (#692)

* Integrate chat from upstream

Substantially borrowed from upstream ref: 13a208ee88e55 (before they
started editing generated artefacts instead of source).

Integrated, including:
  - Remove previously removed features: emoji, hats, and name colors
  - Compensate for lack of unified root template
  - Add React build process to Dockerfile and `bootstrap/init.sh`
  - Preliminary integration of chat websocket workers

For testing, modify `supervisord.conf.dev` to put chat on port 80 and
the site service on some other port. Then visit: http://localhost/chat

Still to do:
  - Access control for specific small-groups (and admins probably):
    Set the values somewhere (site_settings.json? Redis?) and use for
    authorization in `chat_is_allowed`.
  - Proxying only /chat to the websocket workers
  - Chat persistance across restarts: either Redis devops or to DB

* Add nginx server to do appropriate redirection.

* Add necessary columns to User.

* Wire up chat permissions.

* Reload chat on source change.

* Add a better structure for slash commands and add/remove functionality.

* Stop putting up previews of slash commands.

* We require more whitespace.

* Strip DMs out entirely, I currently do not want to deal with them.

* Change "Users Online" to just "Users".

* Clean up a little more DM detritus.

* Save chat history in database.

* Remove unnecessary hefty query to the DB.

* Clean up optimistic messages.

* Initial implementation of notification icon.

* Update readme a little bit.

* Fix notification highlight (mostly).

* Remove chat version number that will never be updated.

* Fix: Errors on logged-out users.

* Add function to nuke the chat state.

* Update DB.

* Add a dedicated deployable docker image.

* Fix: init_build.sh execute bit not set.

* Whoops, screwed up the abort() call.

* Relax chat rate limiter.

* Remove a somewhat silly comment.

* Remove an unnecessary g.db.add().

---------

Co-authored-by: TLSM <duolsm@outlook.com>

bootstrap/init_build.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+set -euxo pipefail
+
+cd ./chat
+yarn install
+yarn chat
+cd ..