connectors should define a <connector>Streams class

Many of the connectors use an idiom of defining a "<connector>Streams" class: Command, File, Http, Jdbc, Mqtt.

Connectors that don't follow that idiom: iot, iotp, kafka, pubsub, wsclient

I think it would be good for all connectors to follow that idiom (we can deprecate the non-compliant classes if we must).

Note, the wsclient (websocket) connector has more issues covered in another JIRA.