Restore spring-boot-starter-ws

Rename spring-boot-starter-webservices back to spring-boot-starter-ws.
Unfortunately the starter exists in Spring Boot 1.3 so we can't rename
it without consequence.

See gh-5711

spring-boot-samples/spring-boot-sample-webservices/pom.xml

@@ -26,7 +26,7 @@
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter-webservices</artifactId>
+			<artifactId>spring-boot-starter-ws</artifactId>
 		</dependency>
 		<dependency>
 			<groupId>jaxen</groupId>