Some changes to file IO

Assimp + some file IO and importer work

Fixes for resource manager

Some work on the content browser

Prep for making content browser in editor

MVP for rendering for now

Jigging around the material system to get it minimally functional

Some work on getting materials ready for rendering

WIP materials

Some resource updates

Some work on resources/VFS needed for materials/shaders

Grid now rendering correctly

Rendering issues fixed

Some WIP rendering stuff

WIP PSO