The Canvas is now single node, instead of having multiple canvases for each frame. This should also be a performance optimization, since there are less canvas nodes, so there are less _input() calls. It should also fix a rare Undo/Redo issue with motion drawing and making lines. Could be unstable, needs more testing.
As a side effect, the guides are now the same for all frames, so this should also close #246.
his means that, if you have a brush largen than 1px, you can draw on the edges of the canvas. All pixels that are being drawn outside of the canvas will still have no effect.
