#10 Add scrolling to tile tool canvas area.

[LunySoft]

A a scrolling control to the canvas area, where the tiles get droppped onto.
this way the canvas can be bigger than the dialog.

Question: Should the canvas be of fixed size, of controlled by user with some width/height tools.

Also if we need another width/height tool, then I think it should be black boxed into a single tool that can be re-used within the different dialogs.