Ensure that spring-boot-starter-ws pulls in the right version of Spring

Prior to this commit, when used with Gradle, spring-boot-starter-ws was
pulling in the versions of spring-jms, spring-oxm, and spring-tx that
Spring WS depends upon, rather than using the Boot’s Spring version.
It’s ok at the moment as both Boot and Spring WS depend on Spring 4.0.5
but will cause problems if we upgrade to 4.0.6 before Spring WS does.

This commit adds explicit dependencies on spring-jms and spring-oxm so
that Gradle pulls in the correct version (as long as a transitive
dependency doesn’t pull in a version that’s greater than the version
Boot’s using).