More Model Improvements & some other tweaks

Other Tweaks:
* fix rendering of shadows so that things like hand and collision proxies aren't rendered in the shadow map

Model Improvements:
* Store the models in the octree element that contains the full bounds of the model
* correctly move models to new octree elements when they've been changed (moved or scaled) to no longer fit in their current octree element
* add options to render visualizations of the model bounds and containing element