Add Hibernate 4 sample

Add a sample showing how Hibernate 4 can be used if necessary.

See gh-2763

spring-boot-samples/pom.xml

@@ -45,6 +45,7 @@
 		<module>spring-boot-sample-devtools</module>
 		<module>spring-boot-sample-flyway</module>
 		<module>spring-boot-sample-hateoas</module>
+		<module>spring-boot-sample-hibernate4</module>
 		<module>spring-boot-sample-hornetq</module>
 		<module>spring-boot-sample-hypermedia</module>
 		<module>spring-boot-sample-hypermedia-gson</module>