Support setting queue,hidden as exported port metadata

[jonnor]

Right now have to use the programmatic API,
or noflo-runtime-msgflo --option=inports.in.queue=foo

Using port metadata, would allow it to be visualized and edited in Flowhub, and be less verbose setup

[jonnor]

Or perhaps queue name should only be in the outer (msgflo) graph definition?
In which case it would be edge metadata?