Generate FinagledClient and FinagledService for java-experimental

Support was probably broken in commit cad09af796 when
the *Client and *Service classes were moved out of the "main"
service file. This change was reflected in the generated Scala code,
but not in the Java code.

See also: https://groups.google.com/forum/#!topic/finaglers/W4hhEcAbocI

- Configure compiler to output generated *Client and *Service classes
  to file
- Rewrite relevant Java generators so that they generate code
  compatible with a class living in its own file
  (import statements, remove "static" keyword etc)
- The "main" service class has a FinagledClient which extends
  (...ServiceName...)$FinagleClient, like in the Scala generated code.
Yup. That's actually what's happening here (bringing java in sync with scala, and nothing else). In Scala, Scrooge generates an object MyService { ... }, which contains an inner class MyServiceFinagleClient. A Scala object with an inner class is the same as a public static inner class in Java. (I think it's like that?)