Petclinic doesn't work with Java 8

RSS is becoming outdated, JSon is a better example

- added json-path to pom.xml
- added a simple test for Veterinarians

Also had to make changes because Spring now uses com.rometools for RSS
feeds
See here for more details: https://jira.spring.io/browse/SPR-11893

 * The old datatables-servlet2 dependency has been removed from the pom.xml
 * Some attributes have been renamed (e.g. paginate => pageable)
 * Starting from the v0.10.0, all web components (servlet, filter) must be explicitely declared in the web.xml file. That's why I added the following declaration: DandelionFilter, DandelionServlet and DatatablesFilter
 * Added a new datatables.properties file in order to disable the asset management brought by Dandelion-Core. This is equivalent to the old cdn=true table attribute