Tiny bit more work on navigation mesh serialization. All I have time for for now.
Add more untested navigation mesh serialization functionality.
Fix a bug where depth testing was disabled when drawing blended transparent objects.
Update CHANGES.
Finish adding basic integration of navigation meshes into the scene editor.

This addresses issue #68.
Improve the look of the navigation mesh visualization in the scene editor.
Improve the look of the "Build" button for navigation meshes in the scene editor.
Update CHANGES.