Rename tuples of SUBSCRIPTION_STATES

(one collided with a real choice !)
Base of jobs+workers, with a worker to fetch repos of a just logged user
Add delayable job/queue/worker and split core.tasks in a module

The Delay* stuff will be moved later in redis-limpyd-jobs
Add a task to fetch closed issues by slices of 20 every minutes

And rework the tasks module tree