proper behavior of Scheduler Service in clusters

In preset when a Schedule is unregistered the quartz job is deleted from database. That's fine for a simple deployment, but in cluster mode that means that when a node is shutdown the jobs will be removed even there are still other nuxeo nodes running.

One way to handle this is to clean up nuxeo jobs from quartz tables when SchedulerRegistryService is activated instead when the module that contribute the schedule is unregistred.