DATACMNS-588 - First draft of Spring Sync integration.

Added Spring Sync as optional dependency. Provided Spring Data based SPI extensions for Equivalency (using Spring Data mapping metadata for the detection of an identifier property) and a highly work-in-progress one for PersistenceCallback as CrudInvoker currently doesn't expose enough API to support the collection manipulation scenarios. Item resource based manipulations should work fine though.

Added a JavaConfig class to set up all the necessary bits and pieces and expose the Spring Data backed SPI components as Spring beans.