Very cool, thanks for sharing! Interesting you work with bones hidden.
As Shiu mentioned, pressing shift while dragging a new bone will parent the image under the mouse to the new bone. Also you can press P then click a bone in the editor or tree, which is faster than drag and drop.
More tips... You can multi select images in the tree (click then hold shift+click again, or ctrl click) and drag many images into the editor area at once. You can press plus/minus to change draw order, so you don't have to use the tree. Don't forget right click toggles to the last tool used, saves time clicking tool buttons. When adjusting bones you can use the Create tool and hold alt to redraw an existing bone.