Polish spring-ws-support's dependencies

* Use separate API and implementation dependencies for JavaMail. This paves the way for JavaMail 1.5 where `javax.mail:mail` is no more.
* Exclude the mail dependency from `mock-javamail` to avoid having multiple copies on the classpath
* Exclude the Geronimo JMS spec from ActiveMQ as the official `javax.jms:jms-api` artifact is already available