Move delete support into FileOperationService.

Refactor Jobs to work with files from multiple providers.
Don't shut down threadpool until service#onDestroy is called.

Bug: 26696797, 26462789, 26567205, 25162803, 26714663
Change-Id: Id43e8e3dc2294cd07dcd6a3477b19efb298c260f
21 files changed