create AssetManager

[ng-daniel]

Complete the Assets module, which contains the AssetManager and loader classes for Meshes, Models, Shaders, Textures, and Materials.

Everything is kinda figured out besides materials, which will require reading more into how the assimp library works and how materials are stored in common 3D file formats.

[ng-daniel]

End-to-end asset loading is good, has serialization, generating metadata files, and support for different types of asset importers. Currently it's just texture importer that's implemented.

Shader importer should be easy, and I think Im gonna do Models, Meshes, Materials all at once, which is gonna take a lot longer because then I have to figure out how to handle sub-assets.

[ng-daniel]

Finished shader loader, also made some fixes/additions to complete + verify end-to-end asset loading (asset data is accessible at the application level).

Need to do model loading. Read up on GLTF file format. Gonna get to cooking.