HornetQ starter

This commit provides a spring boot starter for the HornetQ JMS broker.
`HornetQAutoConfiguration` provides a `javax.jms.ConnectionFactory` that
integrates with HornetQ if none is present and if the necessary HornetQ
classes are present in the classpath.

The connection factory connects to a broker available on the local
machine by default. A configuration switch allows to enable an embedded
mode that starts HornetQ as part of the application.

In such a mode, the `spring.hornetq.embedded.*` properties provide
additional options to configure the embedded broker. In particular,
message persistence and data directory locations can be specified. It is
also possible to define the queue(s) and topic(s) to create on startup.

Relates to gh-765