Add multiplayer menu

[Nemrav]

Adds an initial MP menu consisting of a direct connection tab and a host tab.

• Entries made in the direct connection tab are saved in plain text to a config file ips.cfg (this could change if we add accounts).
• When the player clicks to join a game, the entered IP is validated, a password entry prompt is shown, and a dummy error popup is shown.
• No actual networking functionality. There are a couple functions defined which for now print the player name, password, and entered ip where this should be added later.

[Spartan322]

Could you also capitalize Add in the commit message?

[Hop311]

Very nice PR!
Spartan's explicit type comments, while correct (we should always use explicit types in GDScript, even just Variant when we want to allow something to be multiple types), have resulting in some things breaking. Please test this yourself by deleting (or renaming, if you want to save it for later) your ips config file at %APPDATA%/OpenVic to run the game as a first time MP user