Enhance guice-persist to allow external data sources

_From [rgarcia@dridco.com](https://code.google.com/u/115156493272391760858/) on May 24, 2012 10:16:33_

I believe EntityManagerFactory expects a Map in its #createEntityManager call, on which you could provide an external java.sql.DataSource instance.

I would like to, within guice, `@`provide a DataSource, and on the same module, setup JpaPersistModule with this DataSource.

An enhancement: change java.util.Properties for the actually expected java.util.Map

An issue: how to provide a DataSource, and then inject it to a Map, and then inject it to the actual JpaPersistModule?

_Original issue: http://code.google.com/p/google-guice/issues/detail?id=706_