Biome-Selective models

[Drullkus]

requested by user Titus Armillius on mmd discord.

I'm thinking we should have models that'd change based on a biome, based on a similar filter system like we had for EDGES and EDGES_FULL. Maybe in the ctm bracket in the model.json

[DnatorGames]

It would be awesome if there was an option for textures to recognize one biome from another.

Such as adding seashells to sand while on beaches, and skulls to sand in the desert. :)

[ChloeDawn]

This could be handled under #50 (Implementation will differ from my suggestion in the ticket). A texture could be proxied to another when within a certain biome. The latest suggested implementation is for a multipart-esque form, where multiple proxies for multiple conditions could be defined. A texture could have metadata for a ctm texture, but also proxies to differing ctm textures when biome predicates are met.