DATAGRAPH-458 & DATAGRAPH-460 : Changes for Spring 4.X compatibility

@jexp Changes to make SDN Spring 4.0 compatible. Note, as the Jira regarding the regression introduced in Spring 4 via the ObjectToObjectConverter and FallbackObjectToSpringConverter is still outstanding (https://jira.spring.io/browse/SPR-11693), I added the Spring 3.2 version of the functionality back in (in addition to Spring 4 version) via the class Spring3ObjectToObjectConverter. Should Spring get updated we can remove this but for now this will allow both Spring 3 and 4 functionality to co-exist in a backwards compatible manner.