The beginnings of a JPA datasync system. Everything is subject to change!
Added test for conflicting update response
Added test for pushing non-conflicting update

I had to change the date field in the entity to be of type Timestamp, because
java.util.Date.equals(java.util.Timestamp) is always false, and this was tricking
the state comparator.
Added more scenarios to cold sync requests and responses
Added ability to delete pre-existing entities in sync request