Use realtime database

[timwis]

Problem:

• Currently each new client requests /api/messages from the server, which fetches the most recent page of messages from twilio. There's not currently a way to get more messages
• There's no foreseeable way to store which user sent the message
• We need to add multi-user authentication, so we'll have to have some sort of database anyway, and it'd be a pain to code that functionality

Proposed solution: a realtime database (pouchdb/horizon.io)

• On server start:
  • If db empty, fetch the most recent 3(?) pages of messages from twilio
  • If db not empty, fetch messages since the latest record in the DB (may require multiple requests)
• Auth handled by built-in auth system in db
• Outbound requests from client get put into an outbound namespace. The server listens for new messages here, sends them to twilio, and updates them in the DB
  • This may provide a solution for #2 as well
• Inbound requests work completely differently; they have their own REST route, validate that the request came from twilio, and add the record to the db.

[timwis]

In progress. Track it at CouchDB Milestone