Add network discovery

[Jenna1337]

Add support for Simple Service Discovery Protocol, and Universal Plug and Play.

Don't forget to add settings to enable/disable them as well.

[Jenna1337]

Note: a custom multicast protocol might work better, since SSDP and UPnP seem fairly complex and over-engineered.
All it needs to do is advertise its IP address, port, and text identifying what service it is. A simple text JSON format would suffice.

[Jenna1337]

See https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml

[Jenna1337]

We can use the multicast address 239.81.37.120.
See also: https://learn.microsoft.com/en-us/dotnet/api/system.net.sockets.udpclient.joinmulticastgroup?view=netframework-4.0#system-net-sockets-udpclient-joinmulticastgroup(system-net-ipaddress)
and https://learn.microsoft.com/en-us/dotnet/api/system.net.sockets.udpclient.dropmulticastgroup?view=netframework-4.0

also, since the IP address of the server should be the same as the multicast packet source, we may not need to include an IP address in the UDP data; it could be just the port and the name/description/identifier of the service.