Starting writing a Walls class to contain an array of all of the walls on the screen.  Iterator currently not working.
Manual iterator.
Update unit test.
Fixed wall and successfully ran the unit test.
Walls.next() returns a 4x1 integer array for the wall positions instead of a Wall object.
Create a wallSet object and add a single wall.
Use new collision method for reversing the velocity.
Fixed two runtime errors with Walls.
Set the initial wall generation to be relative to the screen size.
Change wall to stretch across screen at 1/3 height.
Temporarily disable main in Walls.
Accidentally removed the position updater.
Walls now has actual iterator.
Draw the walls as white lines.  Moved wall initialization (for now).
Used new Walls iterator.
Added correct wall bounce for horizontal and vertical walls.
Offset ball on bounce to prevent overlap.
Add onResume and onPause for Sensor in MainActivity.
Implement gravity sensor.
Adjust creator method.