Now that santad<->SantaGUI work more like the client/server they are,
having an SNTXPCConnection 'client' validate its server is no longer necessary.
Having the validation in the 'server' only simplifies the code.
Instead of having santad create a listener for SantaGUI to connect to
and then reverse the client-server relationship, have SantaGUI create an
anonymous listener that it sends to santad using the control interface.
Also add a queue for notifications so that blocks that occur while
SantaGUI isn't running will show up once it starts.
