Screen share across subnets

[izzyalanis]

Not sure if others are interested in this, but I wanted to screen share with a rM device on a separate subnet that could not directly receive the UDP broadcasts from the rM. I made this change to help me do that. It's a little bit of an invasive change, but basically it ssh-es to the rM and uses netcat to listen for the UDP broadcasts on the device itself. Unfortunately the version of netcat already on the rM is hobbled, so I added the logic to install a traditional unix netcat. Do with it what you will.

[Eeems]

It's a little concerning that there is no way to verify the validity of the "traditional unix netcat" binary you included in this PR.

I would not be comfortable myself merging this as-is, and I'd instead want to have the source of nc included and build here so we can confirm that it does as we expect.