Limit scheduled jobs to 100 per app

Packages that are entitled to schedule jobs on behalf of other uids
are not subject to the limit.  Also break the JobStore's monolithic
set of jobs into per-uid slices for efficiency and orthogonality.

Bug 27150350

Change-Id: I8f5f718bf200d55f9977a6fc53b7f617e7652ad9
3 files changed