Change the repo structure to support multiple JVM shell front-ends

The repo structure can have wrappers for multiple shell front-ends.  If someone prefers Scala, Clojure, Jython, etc. to Groovy, the concept is still basically the same.  A front-end script sets up the Java CLASSPATH, and the REPL shell needs to be invoked.

I added a starting point for the Jython shell (v2.5, but v2.7 is getting close).