Adding support for UPnP

[guyluz11]

As this package is suited to bring the programmer a lot of network tools in one place it will be nice to add support for UPnP

There were several UPnP dart packages in the past but they are not maintained, I have found (and tested a little bit) a new package named upnp2 that picked up from the old ones.

Let's add support for searching UPnP devices in the network using the discovery method from that package.

[git-elliot]

@guyluz11 can you more specific use case here? I can't support everything whatever that package provides.