Allow extensions to offer home page (and preferences?)

[timbl]

Extensions which provide views in the data browser world should be able not only to register their views, and they mintNew() functionality, but also components for a person’s home page for others to see, and maybe (less obviously) a component for the person's private preferences. (The preferences UI could be embedded in the app itself, where the user knows how to find it. the home page things which other users see on YOUR home page -- your blogs, your bookmarks, etc -- need to be injected there.)