Point and motion

Added start screen for MotionTrackingJava and changed Projection matrix calculation. Please review this @samtstern. If you give a go ahead, Ill make similar changes to Area learning and point Cloud as well
If we have a `Button` that we don't ever use again after `onCreate`, it doesn't need to be a member variable of the class.  Instead, we can just do it in one line like this:

`findViewById(R.id.first_person).setOnClickListener(this)`.  I think this applies to the first/third/topdown buttons which are never used after we set the click listener.  Then you can remove `private Button mFirstPersonButton` etc, reducing the lines of code.