First stab at device idle mode.

Introduce a new device idle controller service that
monitor's the device state and determines when to go
in to idle mode.  When in idle mode, all we do right
now is turn off network access the same as we do for
power save mode.  Many more things should come in the
future -- stopping the alarm manager from scheduling
(most) alarms, telling GmsCore for it to stop doing
stuff, etc.

Battery stats now has state tracking for devie idle
mode, as well as events for the reasons we can come
out of idle mode (significant motion or the device
becoming active).  Also added new events noting when
packages are installed.

Renamed the "low power" event in battery stats to
"power save" because the former was just way too
confusing.

Finally, fix buffer size reading kernel wake locks.
(Stupidly, just increasing the buffer size.  Ideally
we should try to be smarter and grow our buffer to
fit the data available, but I'll leave that for
another time.)

Change-Id: I0be2062466c83ee9d890c6cf5a228d9cc4090eca