Add support for Spring Rabbit (via Spring AMQP) to Boot

- If RabbitTemplate is on the classpath, turn on autodetection.
- Create a RabbitTemplate, a Rabbit ConnectionFactory, and a RabbitAdmin if **spring.rabbitmq.dynamic:true**
- Enable some **spring.rabbitmq** properties like host, port, username, password, and dynamic
- Add tests to verify functionality
- Add Groovy CLI functionality. Base it on @EnableRabbitMessaging since there is no @Enable annotation for Rabbit. Add spring-amqp to the path.
- Create rabbit.groovy test to prove it all works.