Added regular expression based MQTT topic to AMQP exchange and routing key mapping.

The extension includes working Java unit tests (https://github.com/jschwertfeger/rabbitmq-mqtt/commit/f982dfc22c0cfe5da3cfd314992cd207d30da14a#L8R407).

However, in order for the tests to work the MQTT section in the server configuration needs to define these two mappings: https://github.com/jschwertfeger/rabbitmq-mqtt/commit/f982dfc22c0cfe5da3cfd314992cd207d30da14a#L4R14

Since it seems like `rabbitmq_mqtt.app.src` is used as the default configuration I commented them out in there. I assume you define a custom server configuration somewhere just for tests? This is where this config should actually go but I couldn't find it.

Once that config is moved you can uncomment that Java tests.