Resource Browser

I've started work on the resource browser which will hopefully make it a lot easier to find and place resources inside of the editor. Eventually, this will feature usability features such as tagging, searching, collections, and sorting but for now, it's pretty basic. There is a button in the editor to trigger the building of the thumbnails but eventually this will either be done by the asset server or by some sort of caching mechanism. For now, this works fine for me. Once you generate the thumbnails, you don't have to do it again, they just load with the editor.

Currently, you can actually drag/drop each of the mesh resources into the viewport to have them appear which is a lot easier than creating an Entity scene object and then changing the mesh reference. This is a lot more visual and fits in with the "You need to be able to build a scene with the mouse" motto that I am going for with this editor.