Changes

* Create a progress bar which includes percentage complete of model and texture loading.

* Add particle system size attenuation.

* Allow users to specify texture filtering

* Delete texture objects when textures are deleted from library.

* Create and post a hierarchical diagram of the library classes

* Investigate overriding spacebar and arrow keys from browser's default behavior.

* Add option to change back-face culling.

* Add option to use orthographic projection.