Figure out how to add discourse to local dev stack

[wilson29thid]

Currently we have a docker compose file that enables us to get the full stack up and running with a single command docker-compose up. Discourse's docker setup is very unique and incompatible with this approach. You still need system dependencies. So I'm not sure how we'd add it to the local dev stack, which may be necessary to login (see #446).

Ideas:

1. Use the bitnami discourse image (not supported by discourse but a big company)

2. Create our own docker image that essentially replicates these local dev instructions

3. Run a staging version of the forums and have devs use that to login (shared)

[wilson29thid]

I made a start on option 2 and it wasn't too difficult: https://github.com/29th/discourse-docker