Front-end: convert VisualBase derivatives to BB views

[nmashton]

A quirk of the JS (which I didn't change / fix while working it over for MD and IL) is that Backbone Models are used for the visual elements on the page rather than Views, which would be the more idiomatic choice.

It shouldn't be too hard to refactor the various VisualBase derivatives so that they use Views instead of Models, and this would make the project more maintainable (by removing a hurdle for Backbone developers).