Asset Viewer

Editor requires an asset list and selector to be able to apply to the current scene.

Requirements:
* As a user i should be able to see all resource paths listed in gameinfo.txt
* As a user i should be able to select a resource path and browse its contents
* Browsing a resource path should be laid out as a directory tree in a left pane, and thumbnail preview of all items in the current directory on the right
* Materials should have a thumbnail image in directory view
* Models should generate a thumbnail
* Selecting a resource should provide a means to recognise the selection
- [x] Add list of resource paths to top level directory
- [ ] Create a generic directory tree view
- [ ] Create directory tree when resource path selected
- [ ] Populate directory with file names in current list
- [ ] Add thumbnail for materials