Proper Model Ray Picking

* adds support to Model class to allow ray intersection testing against the actual triangles of the model
* adds JS api for "precisionPicking" to allow callers to control whether or not the model ray picking will be done down to the triangle level
* changes the entity scripts for clicking and mouse down to use precise picking (unless disable by a developer menu)
* changes editModels.js and newEditEntities.js to use precision picking when clicking to select