Add option of force delete running/idle/queued jobs

[capitancambio]

Sometime some jobs will remain with these statuses after a crash or a force shut down. Add a flag to the delete api so we can force the deletion

[capitancambio]

see daisy/pipeline-framework#105

[josteinaj]

Would this allow stopping of jobs that are actually (not apparently) running as well? If not, what would happen if one tried?

[capitancambio]

That's a really good point. It might create some unexpected behaviours and it might leave some files unaccounted for. This is not a good idea, I'll roll back to the clean at start up time approach.

[rdeltour]

Merged.