Add Quick Settings USB Tether tile (2 of 2)

Patch Set 8: Make tile dynamic

- Thanks to Björn Lundén for the drawables

Change-Id: I414848f6cb8a789d0b5edfcb79ab53cb85ebc20e
Merge branch 'cm-10.1' of git://github.com/CyanogenMod/android_frameworks_base into cm-10.1-n7