[server] Implement lobbies

[lunacys]

A lobby is a "room" for players that will play together (free-for-all).

Each lobby consists of:

• Unique identifier (UUIDv4). May be used to join lobbies (both public and private).
• Lobby name.
• Player limit - max amount of simultaneous players.
• Joined player list - username, role.
• Creator/owner username.
• Whether the lobby is started (match is ongoing).
• Whether the lobby is public or private.
• Game Settings (explained later).

Lobbies are stored in memory without any sort of persistence.
Each lobby (probably) should be in a separate task/thread.

Any player (client) may create a lobby, but simultaneous lobby count is limited to 1 per user.
If a player leaves an empty lobby (i.e. there only was him and nobody else), the lobby gets removed.
Otherwise if at least 1 player stays in the lobby after the leave, he becomes an owner of this particular lobby. New owner is chosen randomly.

The owner, and owner only, may start a new match at any time.
Each match may have different game settings. See the structure below:

Quader/src/engine/src/game_settings.rs

Line 93 in c552734

pub struct GameSettings {

Owner is able to change settings at any time if the lobby is not started.

Only authorized users may join and create lobbies.

Subtasks:

• Basic lobby creation
• Ability to create and join lobbies
• Ability to change lobby settings (name, player limit, publicity)
• Correct lobby handling (lobby count per player, lobby invalidation, etc)
• Support for custom game settings, as well as changing it on the fly is the lobby is not started
• Check user authorization