Right now widget config windows all have the same size; changing the size for one and then opening another one causes that other one to open with the size that the first one was closed with (or at least, it will once the regression described in Bug 488206 is fixed).

This isn't ideal since the contents of these windows vary widely. A minimal widget with only a few settings benefits from a small window, while something like the wallpaper chooser benefits from a large window.

Accordingly, it would be good to make each widget able to choose its config window's own size, and for those sizes (and on X11, positions too) to be remembered on a per-widget basis.