Move OrderedSet.pop out of the __specials__.
Expose OrderedSet's first and last items.
Let users of OrderedSet iterate complete triples,

i.e. (curr, prev, next) items all at the same time. It makes sense,
    since we do have them.
Add active_colors.

Also format the colors with wider lines; 100 columns are accepted.
Widget width and height define bounds!
Refactor handlers: use decorator, don't pass self.
Image and Label: bounds are set by Widget now.
If the key is None, don't try to translate it.

It simply won't work, and will cause an error instead. Oops?
Remember how self.placement is parent-relative?

Yeah, maybe the widgets should behave as if it were. Oops.
Add most of the List implementation.

Still needs stuff for changing the active list item and the like.