Provide Clojure implementations via esfj library.

I've written a small library named "esfj" for providing a tiny amount of Clojure integration for JSR-330 dependency-injection frameworks such as the grapht framework used by LensKit.  It allows injecting Clojure functions into the dependency graph as "Providers" -- essentialy factories -- of instances of classes in the graph.

This pull request updates the stub project to use esfj to move the student-edited code from Java to Clojure.