Adding accessibility support to the Status Bar.

1. Added content description to pretty much all animals
   in the zoo including buttons in the navigation bar,
   notifications and status icons for battery, signal,
   data, etc.

2. Rectored to avoid ovelaying views since they block
   touch exploratino. In general overlaying views
   cause trouble for touch exploration and accessibility
   in general.

3. Avoid sending accessibility events in case the user is
   touching outside of the StatauBAr panels to avoid
   confusion.

4. Added records to accessibility events in the places where
   this would help the presentation. So the event comes from
   a given "leaf" view and its predecessor is adding a record
   to the event for itself to provide more cotext. It is up
   to the accessiiblity service to choose how to present that.

bug:4686943

Change-Id: I1c1bd123d828fb10911bca92130e9a05c1f020b3