Stop polling for pending jobs

**Problem**
Once a job is triggered by press on the build/other servers (Archive, New Bench etc.), a job is created on the press worker that polls for job status every 5 seconds (via [hooks](https://github.com/frappe/press/blob/master/press/hooks.py#L245)).

This problem causes obvious load on the servers.

**Solution**
Using sockets in agent (out of the box with [flask-socketIo](https://flask-socketio.readthedocs.io/])).
We also need to use gunicorn with eventlet. To allow for async connections

Steps
- Once a job is triggered by press on the server create a on_[success, failure] callback.
- These callbacks will trigger events / [emit](https://flask-socketio.readthedocs.io/en/latest/api.html#flask_socketio.emit) which let the client know the status of the job.
- This also requires a pub-sub mechanism as socketIo will have to emit these callback events from rq-worker processes.

**Problems caused by the solution**
- Job's have a certain order of being processed once completed this might break for which also needs to be address.