Added liquibase autoconfiguration for database migrations

If Liquibase is on the classpath it will fire up on startup. Various
config options are available (as well as the option to disable it).
Liquibase uses a YAML format for changes (in classpath:db/changelog).

spring-boot-samples/pom.xml

@@ -34,6 +34,7 @@
 		<module>spring-boot-sample-data-rest</module>
 		<module>spring-boot-sample-integration</module>
 		<module>spring-boot-sample-jetty</module>
+		<module>spring-boot-sample-liquibase</module>
 		<module>spring-boot-sample-profile</module>
 		<module>spring-boot-sample-secure</module>
 		<module>spring-boot-sample-servlet</module>