Changes in DeviceIdlecontroller and JobScheduler to support Auto GarageMode.

Changes made in the cl:
1. Let DeviceIdleController take listeners on whether background
maintanence services are active. This currently includes JobScheduler,
SyncManager, DownloadService. Note this is the last known
states reported by these services.

2. In JobScheduler, make the idle threshold and alarm window configurable.
So in the car case, we don't need to wait 71 mins after screen off
to kick off any jobs that require device idle.

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* We are not going to suppress JobScheduler, DownloadService, SyncManager
entirely while user is driving. Because apps may not be working properly if
these services are suspended.

* The jobs that we don't allow to run while driving are the
jobs submitted to JobScheduler that require device idle.
And this is already taken care of, because
screen is ON and JobScheduler will not consider the device to be idle
while driving (unless user turns off the head unit).

* We will need to give the JobScheduler a chance to run the device idle
jobs when car is turned off. This is the scope of GarageMode. If
DownloadService and SyncManager want to run, we will allow them to run
too.

* The headunit is treated as wall power device, so it's always charging.
The charging state will not toggle.

Change-Id: I55b92cf92efd61c48dd6c9b8197c2b68078a4439