Add support for loading the OBJ model format

[hogsy]

Down the line, during the extraction process, we think it might be a better approach to convert the scenery models to the more "standard" OBJ format as opposed to extending the existing formats.

Pig models and some others will probably remain using the original model format.

• https://en.wikipedia.org/wiki/Wavefront_.obj_file
• http://paulbourke.net/dataformats/obj/
• https://www.cs.utah.edu/~boulos/cs3505/obj_spec.pdf

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• [x] Add support for loading and rendering an OBJ
• [x] Ensure support for dealing with multiple materials

[hogsy]

https://github.com/TalonBraveInfo/OpenHoW/tree/obj-support

[hogsy]

Closing as this is done and basically merged - waiting on texture atlas changes.