Feature request: allow deleting a game

[CrsiX]

If the user is still participating in the game (alive), then the functionality should be resigning instead (see #75). If the user is not alive anymore, it should be able to remove the game from the game list. This needs a server endpoint to remove that player from the list of active players in the game; however, the server needs to remember that this user was participating in the game (i.e. some switch set to false only).

At the moment, there's no such API endpoint available.