You can do it manually without much effort. You could place them into folders like Buildings, Scenery, etc., then place the individual artists' works in sub directories, so you know whose was what. When I'm working on a project I move (actually copy/paste to keep originals where they started) stuff around as such all the time. It makes things SO much easier. For GG to do this is automatically is probably a bit much, as everyone sorts things to their own liking.
MAME Cab PC: i7 4770@3.4Ghz (passmark 9945), 12GB RAM, Win 8.1/64, GeForce GTX645 (passmark 1898); Shiny new laptop: i7 4800MQ@2.7Ghz (passmark 8586), 16GB RAM, Win 8.1/64, GeForce GTX870M (passmark 3598); Old laptop: i5@2.3Ghz, 8GB RAM, Win 7/64, Intel 3000 graphics