Uniformize Occluders and Distractors

[danielbear]

Draw occluders and distractors from a common subset of the model library and in a common sampling distribution across controllers.

IMPORTANT
occluders, distractors, and "quirky" objects should all be models with use_flex=True. This is because only these models have easily accessed meshes that can be used for modeling.

For FLEX-based controllers, such as clothiness (@arty-p), all objects should have use_flex=True.

A way to get all the models that are FLEX-enabled is:

# lib = ModelLibrarian("models_full.json")
# for record in lib.records:
#     if record.flex:
#         print(record.name)

[felixbinder]

I already made that issue here: neuroailab/tdw_physics#40 We decided to leave the stim generation issues in tdw_physics

[danielbear]

thanks!