OGM-370 Pass transaction manager to Neo4j

In this patch I try to pass the transaction manager to Neo4j.
I first look for it in the JNDI, than I use  com.arjuna.ats.jta.TransactionManager.transactionManager().

What it is happening is explained here: https://stackoverflow.com/questions/23824518/how-to-enlist-xaresource-with-existing-transaction

and here: https://github.com/neo4j/neo4j/issues/2522

I've also try to use the same integration tests that we have for the others db but it does not seem to work, at some point it enlists the same xa resource twice. The branch with the integration tests is here: https://github.com/DavideD/hibernate-ogm/tree/OGM-373-Integration-tests


This comment looks a bit scary. E.g. in case of container-managed transactions or CDI's `@Transactional`, surely the operations will be invoked on the delegate and not this wrapper. Does this mean this won't work then?