Java example re-written using idiomatic Groovy

You asked me to write an example using Groovy, so I just took your simple example with Java and re-wrote it using idiomatic Groovy.

Things to note: 

* all code is @CompileStatic - so its all statically typed Groovy, so it generates tight, fast byte-code like Java
* the tests make use of (and the code demonstrates) Groovy extensions that can be used to "Groovy-ify" the Ebean classes without having to change them.