Add More Models to system

[honeybunches-of-oates]

This involves fixing bug inside prefab generation which seems to not be properly integrating with vHAC see issue #15

[yamins81]

We can use Dosch models or potential ShapeNet.

A core thing will be deciding about and getting metadata for the models into a DB that can then be coordinated with environment responses to produce labelled datasets.

Once models are found and it's made sure that they in a standard OBJ format, we need to:

1) run vhacd

2) run import of the model as a unity prefab in the 3dworld project. this has to be done using the Unity desktop interface on a PC or Mac. it cannot easily be run in parallel. but the problem that there is a big in the script in the unity project for doing this which needs to be fixed first -- issue #15

[yamins81]

We also have to make sure that that when the prefab code runs it puts the models a good directory structure in the prefab "props" directory. as per issue #23

[yamins81]

Basically the progress on this as of now is that we've decided to use ShapeNet models (http://shapenet.cs.stanford.edu/) to get a bunch of models into the system. Currently these have all been run through vhacd and the prefabs have been made. however, now we're experiencing a problem getting the prefabs into a resources.assets file during the binary build due to this error:
http://forum.unity3d.com/threads/two-extremely-vague-editor-errors-in-unity-5-1-and-5-2.355607/

So, we've decided to use AssetsBundles as the solution, where we think of each prefab as a different assetbundle.

[yamins81]

@chengxuz is writing a script to make this easier. issues include:

1) IsLight -- always set to 0?

2) anchortype -- always set to "ground"?

3) stackable area -- can this be computed by heuristic?
-- Or maybe objects should be dropped just physically? making a new procedural_generation version?