Record ModemActivityInfo and distribute power blame to apps

Telephony expsoses a getModemActivity() method, which BatteryStats
will poll when a change in network activity occurs (on the modem).

The time spent in various states (tx, idle, rx) are distributed amongst
the apps that did rx/tx traffic during that window.

Bug:23147562
Change-Id: I480a85df95786f87c382b96816fe2ed4bb2d5a42