Commit 03e0ee53d2 removed window shapes, because at the time I was too
lazy to port them from the old image system to oocairo.
This commit re-adds them, but for now only as a way to set the shape.
Signed-off-by: Uli Schlachter <psychon@znc.in>
A drawable is something that you can draw to, just like a drawin. However, a
drawable isn't necessarily its own windows. This will later on be used to
implement titlebars where the titlebars are drawables.
Signed-off-by: Uli Schlachter <psychon@znc.in>