[Feature] Add party system / private game

I think that party system is a must nowadays and should be implemented somehow.

Be able to party with friends so we can play together on the same team and also be able to create a private instance of the game. Say I want to play Spider Bite only between my friends.

I know that perhaps is not a trivial change on how the framework works. Perhaps having a pre-game screen before the game launch were you can see all the instances of the game like a server list and you can select which one to connect.