Make the queue system for the communication between dynohost and apiserver more efficient;

[Filirom1]

Currently DynoHost are doing long polling on the APIServer to get their jobs.

The main advantage is that it doesn't depend on an external component (like a message queue), and in so doing it avoids setup and maintenance complexity.

JobGiver is quite complex to understand and I really don't know if leastBurdenedHost feature works :/

ApiServer poll the database periodically. We may use PostgreSQL LISTEN/NOTIFY to make it better.