Hook, Line and Sinker

I've been making a conscious effort to pepper the Metawidget base classes with lots of subclass 'hooks' - to the point of making more fine-grained methods and classes than I usually would.

This is because I anticipate Metawidget being extended in an unusually large number of ways, by an unusally diverse range of third-parties. They'll be those who want to keep all the components but rework the layout, those who want to keep the layout but change the components, those who want to keep both the layout and the components but alter the validation etc. etc.