Restore connection on reconnect

[elliotchance]

Websockets can be flakey and the idea of the websocket dropping out for even a moment would be disastrous. I believe this can easily be resolved by:

1. When a client connects it should send an identifier back.
2. The connections should be held in a global map. Only expiring/removing connections sometime after they have disconnected (like 10 minutes, or more).
3. When a client connects with a previous identifier it can use that connection instead of calling the newConnectionFn.

This way all state is maintained through dropouts.