My old setup of throwing *all* of the IPC types and opcodes into *one* enum was
becoming unbearable. Now that we have multiple things using the same opcodes
(because they can overlap) I think it's time to repay this technical debt.
This overhauls the structure of the project to move IPC structs into their own
modules, and separate the opcode data/lists into separate ones depending on if
it's clientbound and serverbound.
Nothing has changed functionall, but this is going to make it way easier to add
more IPC in the future.
The current situation of throw-every-piece-of-logic-into-one-file for each
server isn't working out. So now there is a new ZoneConnection/LobbyConnection
struct that will be delegating tasks to their own Handlers (for example, there
could be a ChatHandler.)
I'm not sure how well this architecture will scale, but it's better than what
we have right now.
