Previously, all keydown KeyEvents were accepted, causing parent widgets
not to receive them. With the addition of shortcut handling to keydown,
shortcuts were not called when the ImageEditor was focused.
This patch adds scaling function to the move tool.
When the cursor is over the lower right corner of the layer, it changes.
This is to signify that the layer can be scaled by dragging the mouse.
There is currently no preview of the scaling.
Doing a resize every time the mouse moves leads to unexpected behavior.
