Camera intrinsics unit tests fixes

- Existing test ApplyIsInvertibleSimple was not
  doing right thing - distortion model used there
  was ininvertible.

  Tweaked parameters in a way model is invertible now.

- Added some own tests which tests;

  * Principal point always maps from pixel space to
    zero normalized position.

  * Some basic tests to check whether individual
    apply/invert works correct.