Chek API signatures

Since the Java requirement change between 5.6 and 5.7, we need to check the API compliance, especially because of bug fixes (backports)

Also, we need to check the API of client libraries such as nuxeo-connect-client and nuxeo-automation-client.

Finally, it would be useful to have warnings about Nuxeo platform API changes which should only happen after a deprecation over multiple versions.

=> Make use of animal-sniffer-maven-plugin