[UI] A small change... for a start

[Gary Chambers]

Pinesoft-Widgets-gvc.302 on SqueakMap. Nebraska not included in changes (may do a separate package for that if there is interest).

Added CompositeFillStyle. Canvas double-dispatches to the fillstyle/color/infiniteForm.
Should allow more complex fills through subclassing(like pieced together from forms for a button, top-left image, top image etc.).

Have fun!

Gary