Load xac and xsm with cpp

[Nemrav]

XSM animation file loading:

• Can now read 0xC8 chunk style animations (needed for zulu_walking.xsm)
• Uses a hack of deleting frame 0 from all animation tracks to work. This replicates the behaviour of the gdscript version, but obviously is not ideal.
• Cached in ModelSingleton
• Used for all animation loading

XAC file loading:

• Used for static (ie. no 'unit' script for animation) meshes only currently.
• Textures are loading, but lighting is off
• Bone weights / skinning chunks are not working and needs more work before this can fully replace the gdscript function versions.
• Cached in ModelSingleton