Can't test because I haven't added the "start game" button back yet.

lobby.gd had gotten big, bloated, ugly, and hard to read. It needed a
refactor. The first thing I did is split up the *GUI* into the logical
steps it should be. So the new flow is:

 - Start the game
 - Click "Quick Play"
 - Matchmaking begins on my dedicated server

 - Start the game
 - Click "Custom Game"
 - *Only now* am I presented with server / client options

 - Start the game
 - Click "Singleplayer"
 - Singleplayer

NOW, and only now, and NO MATTER WHAT PATH I TAKE, I am taken to the
*lobby*, which now is where I:
 - Choose my name
 - Choose hero
 - See list of players
 - Get my team assigned
 - Anything else that I might like to put in
The point here is that this has *nothing* to do with handshaking /
matchmaking / etc! This is just part of the game! At this point I have
*already been connected* to the server. I've already been aquainted with
my other players. The game has begun.

I put the things that don't belong in any of these flows in
networking.gd, a sort of model-view sorta thing. All of these flows use
some sort of networking thing like `init_server` that tbh should be
*completely* abstracted from the UI.

It's totally a WIP!!! Above is the IDEA, but below is what I've actually
*done*:
 - Made the scenes, made a passable UI for each one that at least
 indicates ~what they'll do
 - Made the corresponding scripts, and split up the lobby script into
 ABOUT where I think it'll end up, but no promises
It still errors all over the place, and it's nowhere near properly
organized. PLUS, I'd also like to rewrite a lot of the code / rename
things as part of the initial refactor goal of making me able to
actually think about networking.