Parse objects as a scene from input 3D file

[crisbour]

• Construct scene as a list of objects from the 3D file (.obj) instead of having a list of files per object.
• Separate mesh/object loader as a trait, such that the obj, gltf, usdz, etc can be used, but the core functionality of the project should be agnostic to the choice

[crisbour]

Implemented here:

• 0e2afb0
• 60d5994