Improve tethering notification icons

Replaces the stock icons with the ones I submitted as part of
http://review.cyanogenmod.com/#/c/15930/ in CM9.

Change-Id: Iecfae9ad579c6c9ae06da0a08b61e9359a8a37b0
Remove power widget background

Change-Id: I314642782525fc441a651cc2b48b227f663dfeed
Telephony: Add getLteOnGsmMode() method (1/2)

Same functionality as the existing getLteOnCdmaMode, but for GSM
LTE devices.
Enable with the telephony.lteOnGsmDevice system property

From CM 10.0: Ibfb47ca608e51393b99d3308e0a6c66050b3f32e
- Moved getLteOnGsmModeStatic() to TelephonyManager.