Manage the standby bucket in AppStandbyController
Default implementation of bucketing based on simple timeout:
ACTIVE, if recently used
12 hrs to move to WORKING_SET
2 days to move to FREQUENT
7 days to move to RARE
(subject to change)
RARE bucket equates to the old "idle" or "inactive" state for
an app.
Bug: 63527785
Test: AppStandbyControllerTests.java
Change-Id: I970d7afcdf47c31a9413da8fd4852066a13676a2
17fffee490