Support for MQTT channels

[abudavis]

Greetings from Norway!
Unsure if this was previously answered: Is it possible to create metrics for MQTT channels [CHLTYPE(MQTT)]? We have certain applications that only support MQTT and it would be great to monitor them.

[ibmmqmet]

See #132

It's a bit higher up the priority list now, since I have done the AMQP channels. But still not done.