Replace zmq by http
Replace the ZMQ protocol by HTTP for worker<-> server communication and pushing the logs.
The logs are now handled directly by gunicorn that can be scaled easily using a load balancer. This is also the case for handling job state changes.
Both lava-master and lava-logs has been replaced by a small daemon (lava-scheduler) that only do the scheduling whenever needed.
On the worker side, lava-slave has been rewritten from scratch and renamed lava-worker.