Use priorities to select which ScheduledJobs must run

Hey Guys,

Following yesterday Q&A about Jobs I would like to propose adding priorities level to the job queue system.
This should help addressing the mass-update job issue, which we get on some use cases.

We sometime need to execute some logic which will take a lot of time to run.
Of course we chunk it in smaller batches (we create many small jobs).

Each job is well within the one minute cron period.
However if they are created with the same run datetime they will still block all the other jobs from running.

There are ways to ensures this does not happen, but it would be way easier if we could just specify a priority level for each job.

1. A low level job would only run if no higher level job needs to run.
2. Jobs at the same priority level would run based on their date-time.
3. Priorities levels would be integers so that we can adapt how many layers each customer instance needs.
4. Standards Scheduled jobs would have the higher priority (0 ?) but we could still customize it.

Please pretty please?

Best Regards,
Laurent