GTK is increasingly moving away from icons in the menubar, and when we finished the port to GTK3 we lost them in GIMP as well.
This was a controversial change - some people prefer the cleaner interface, while others (like myself) find the icons helpful for identification.
Fortunately, I finally figured out how to restore the icons! It still needs some clean-up to remove the excess spacine, but it works. I submitted it for review and discussion, so we'll see what's decided.
