The uix.Canvas widget now maintains a selected Tool which configures how
the mouse interacts with the (editable) Canvas widget.
The default Tool is the PencilTool and implements the old behavior: it
draws pixels when clicked and dragged based on your currently selected
Color Swatch. This tool automatically becomes active when you toggle the
Palette tab in the editor mode.
A new Tool is the ActorTool which becomes active when you select the
Doodads tab. In the ActorTool you can't draw pixels on the level, but
when you mouse over a Doodad instance (Actor) in your level, you may
pick it up and drag it someplace else.
Left-click an Actor to pick it up and drag it somewhere else.
Right-click to delete it completely.
You can also delete an Actor by dragging it OFF of the Canvas, like back
onto the palette drawer or onto the menu bar.
