Accessibility: Keyboard users can select and move cels

[emhoracek]

Right now the canvas isn't accessible for keyboard users.

It would be cool if you could somehow select into the canvas, maybe using TAB, and then it would select an object. The selection should be visible, but open to ideas on how it is shown. The user should be able to move the selected object by moving the arrow keys. They can change which object is selected by hitting TAB (or some other key) and cycle through objects that way.

If this seems like too big a task, feel free to take just part of the task. For example, you could just do the selection visualization and leave moving the object with arrow keys to someone else.

Ideas for showing the selection from easiest to hardest:

• Draw a rectangle around the cels in the object. (This would look bad, but something is better than nothing!)
• Shift the hue of the cels in the selected object. When drawing, for each pixel, change the red/green/blue values by some amount.
• Outline the visible pixels of the object. This would require you to find the outlines of each cel and combine those outlines, which may be a tricky problem!

(Edited to refer to objects instead of cels)