Implement ability to copy things between levels

[MattFiler]

For now, I'm interested in supporting what I already know I can. More will be supported down the line, but currently I can add support for:

• Composites without resources
• Models
• Textures

[MattFiler]

Composites without resources is now live on staging.

[MattFiler]

Note to self: need to solve proxy export issue with composites.

[MattFiler]

Related: #253

[MattFiler]

Texture porting will be pushed to staging shortly. Models are working but I want to include the option to copy all associated materials and textures with them which is proving more tricky.

[MattFiler]

Going to revisit this soon:

• Improve model/material/texture parsers to depend on actual loaded object rather than write index
• Once that's done, implement porting of all content within asset editor
• When it works, implement into the script editor with support for other required things like ENVIRONMENT_ANIMATIONS

This should provide the base support for porting composites with the important resources.

COLLISION.MAP and PHYSICS.MAP resources are not required for now, as we should calculate these in the script editor when saving. This is also a WIP: #268

[MattFiler]

Successful port of a character - FACEHUGGER. Only ported model and character animation info, no textures - but good progress.

https://discord.com/channels/1116018062630592593/1116020662272807049/1161054061949358181

Tried the same method with RANSOME and it caused a crash, which I suspect is due to some unhandled indexes in the model submesh.

[MattFiler]

Note on this - porting characters quite frequently leads to invisible parts over distance. Digging into this more it appears to be LOD related, as if I use a LODControl entity to force LODs off the issue goes away. I suspect there's an index somewhere relating to LODs that I'm writing wrong when porting.