Rebuild the index Enlive template on each resource load.

This is not the most efficient approach, but it's good for development,
and once we start sending accurate etags again, it won't be too bad for
production either.
Simplify list application in load-list.
Provide update-scope function to Videos controller.

This permits interpolated ng-click handlers in the template along these
lines:

ng-click='(update-scope :section "Foo")'

In idiomatic AngularJS, it is common to have click handlers which
perform direct variable assignments on implicit scope properties; this
reproduces that idiom. It may not actually be the ideal way of working!
Use AngularJS routing to display videos list.

As of AngularJS 1.2, routing is broken out into its own module, ngRoute,
so it was necessary to install and require that module. I also updated
the server-side routes in core.clj so that any URL not handled by a
Liberator resource serves up the index page; this permits AngularJS to
handle routing of URLs such as "/videos/15", while URLs such as
"static/foo.js" and "api/v1/videos/15" still work through Liberator.

Within the Angular routing setup, note the use of `clj-js` to create the
objects ngRoute expects. These routes shouldn't have to be touched after
startup, so I don't care if they're ClojureScript atoms or what.