Separate open seats in a game from players

[j-toscani]

Description (five sentences max.)
In the future I want a game to be a session of four Websocket connections. If one party leaves the table, there should be the possibility of someone filling the open seat. In order to make that possible I want to implement the concept of seats in a game that can be filled. In contrast to players implicitly taking a seat if they are part of a game.

This could also open up the functionality of spectators or letting a game start where not all seats are filled.

Possible implementation
Seat object that holds connections

Acceptance Criteria

• A Hand is not tied to a player but a seat
• If I know the player, I know what cards he holds in his hand
• A game can be started created without all players present
• Players can join and leave a game

Out of Scope
What not to worry/think about.

Document optional improvements
Optional. Could lead to a better feature.