[Project] Set maven parent for this project to ch.eitchnet.parent
[New] implemented a test to allow multiple operations

This test makes sure that updating after adding, or any other operation
in the same TX works properly. Found a problem where the
PersistenceContext didn't implement hashCode() and equals() which lead
to each operation being added even though a previous operation was
already registered
[New] implemented locking for all persistence operations

A LockingTest tests the locking, but still needs to be extended to test
further use cases, but basic locking works.