Add support for power keys, improve behavior of virtual keys.

The platform now knows how to deal with a platform key, which at this
point is "just like end call, but don't end a call."

Also improve the handling of virtual keys, to allow for canceling when
sliding off into the display and providing haptic feedback.

Finally fixes a bug where the raw x and y in motion event were not
always set which caused the status bar to not work.