Summary:
Pull Request resolved: https://github.com/facebookincubator/momentum/pull/199

Add Python bindings for `loadUrdfCharacter()` with two functions:
- `load_urdf()`: Load a character from a URDF file.
- `load_urdf_from_bytes()`: Load a character from URDF bytes

Reviewed By: cdtwigg

Differential Revision: D69280695

fbshipit-source-id: 115c8232662cb3f1bad326b84ea7b9c01ae79074