Migrate away from Wavefront OBJ to support full mesh information

[Xaymar]

The current export format, Wavefront OBJ, is extremely limited:

• Only a single normal layer.
• Only a single texture coordinate layer.
• No bones.
• No weights.
• No supported for vertex colors.

Ideally we should switch to an easier to work with format. glTF seems to be a reasonable option.

[Xaymar]

Exporting models is not available for now. See #23 for progress