I've added ability to drag and drop items form the project treeview to the scene window

So, SceneEditor could have a mesh dragged, or a material dragged onto a mesh (or submesh, whatever checks the editor eants to do).
Also, because of this, I needed a way to identify material definitions in a material file. So, I hacked together a way (has to be a better method) which expands the material file in the project explorer into all defined materials

Also, as a way for a material editor to know whether a material file was selected, or a material definiton, I used the TreeNode.Name as = ResourceGroupname + " " + materialName + ".material_element"
So, to make a material editor work with that extension, just provide make material editor handle the ".material_element" extension, and you should have all the needed info (groupname, and material name, that you could also find the material file name - orgin).