Material toJson fromJson work.

Signed-off-by: John McCutchan <john@johnmccutchan.com>
Camera fixes

Rename MouseKeyboardCameraController to FpsFlyCameraController.
Viewport::aspectRation -> Viewport::aspectRatio.
Clamp FpsFlyCameraController pitch angle.

Signed-off-by: John McCutchan <john@johnmccutchan.com>