Add redis.gem
Submission: Support streaming using Redis

* Submission#stream: subscribe on Redis, yields recieved submissions
* Submission#judge!: Announce on redis after saving
* Submission#kick_judge: Announce on redis
Increate pool size for development DB
Add LiveSubmissionsController for streaming events

- GET /submissions/stream: SSE endpoint with submission section html
                           without judge results
- GET /submissions/detailed_stream:
                           Same with above, but includes judge results