UPnP support

[diegodlh]

I haven't delved into the Jamulus code base yet to propose a solution myself, so I'm posting this here as an open question/suggestion in case someone can pick it up.

UPnP support (that is, automatic configuration of port forwarding for the server) was suggested in the Sourceforge discussion forum long time ago, but finally rejected with implementation of central servers.

However, the central server solution does not always work, and in some cases (such as when clients are behind carrier-grade NAT) port forwarding has to be configured for public servers as well.

[gilgongo]

This is great idea but probably needs some discussion on how best to spec it up for an actionable work ticket. To that end, I'll move it to a discussion so as not to clutter up the Issues.