Database Migrations

[goto-bus-stop]

For #401, #303, and to prepare for future database changes, it would be great to have a database migration thing set up.

I think it will be easiest for us if we make these migrations run at boot time, with avvio… We have to decide then if/how we handle incoming requests during the setup phase, eg:

• Do nothing and let the reverse proxy figure out that the API is unreachable
• Have a temporary server that just responds with a JSON-API Service Unavailable response

It looks like https://github.com/tj/node-migrate could be a handy library for doing the actual migrations. We can write a MongoDB-based migration storage.