Add Quick Settings USB Tether tile (1 of 2)

Patch Set 3: Hide the tile if USB Tethering is not supported
Patch Set 4: Make tile dynamic

Change-Id: I43fec8c3264b89b647f1626b8d29e459e78672ab
Merge "Add Quick Settings USB Tether tile (1 of 2)" into cm-10.1
Merge remote branch 'cm/cm-10.1'