Add adjustable trigger area for the @ppbar.  Users can define the width, height and Y position of the trigger area.  Only this area will receive touch events. [1/2]

Patch Set 2:
  Make enableKeyEvents and disableKeyEvents return the flags used and
  use reduceToTriggerRegion and expandFromTriggerRegion.

Patch Set 3:
  Use a nicer looking shape drawable for the trigger region when
  visible.

Change-Id: Idcd27bc70d95841ebcbef178a986c77098adfb09