Asset Browser

[snake-biscuits]

QtPyHammer needs a UI element to select textures and assign them to selected faces
See the project for a rough outline of what needs doing / is done already

work with @snake-biscuits to figure out how to attach the UI & tools to a selection
since they will be working on selecting in 3D for #7

[snake-biscuits]

Sketched out a new design for the layout of the AssetBrowser class
I plan to get all the background work (.vmt parsing, textures in the viewport) done before april, but we'll see