Some minor changes in order to use it with TomEE

Hi Antonio,
I was able to run your awesome Demo application with the Apache TomEE server. I needed to do two minor changes though. Please consider a merge if you think it is ok.

-DBPopulator.java -> removing derby dependency. it will be defined by the server
-ExceptionInterceptor.java -> Serializable objects should have serializable fields.

[]s,
Thiago.