Jython Shell Improvements

This will be a longer-lived pull request; some of the ideas are still in the speculative stage.

The specific ideas:
* Syntax highlighting.
* Some form of code completion.
* Trying to make the GUI less clunky.
* IPython-style wrapping of things like lists with many elements.
* Hotkeys.
* Getting the underlying implementation to understand and use repr; rather than dooming the user to a life of "print blah_obj".
* From Mike: a "run script" action that circumvents any clunky copy/paste requirements.