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.
They are all in use actually... unless I've missed something...
Service is used in finagleClient.java line 41 (using the full com.twitter... namespace though)
SourcedException used in finagleClient.java, line 89
Counter used in line 109

Service is used in line 41, but is fully namespaced, so we don't need to import it.
NullStatsReceiver is not used at all. I'll remove these two.