MotoActions: Use stow sensor for both hand wave and pick up gestures

MotoActions: Use stow sensor for both hand wave and pick up gestures

 * The behaviors of stow and proximity sensors are pretty similar, so
   there's no need to use both at the same time. Simply use the stow
   sensor to handle both hand wave and pick up gestures.
 * Switch to timestamp associated with the sensor event to determine the
   operation while at it.

Change-Id: I39767cf7b2e48bc2b0baabfac1e47240012f71d6