Power widget & tether: Restore ICS drawables, replace/create xhdpi drawables

This restores the ICS drawables because they fit better. Some icons by prash
was kept slightly modified and quite a few new ones.

Also replaces the tethering notification drawables as the stock ones
are too big.

Change-Id: I49e1e457fd931b38b5cf16fbeb3b8c58f0b66331