#34 Game/Lobby functionality

[Hanno Braun]

Many online games rely on a lobby, where players can meet and start games which are then separate from each other. The framework should provide functionality to support this.

The following functionality should be provided:
* Define all network messages that are needed (like query for games, games status (open/closed), join a game etc.)
* Provide nice APIs, both client- and server-side to access this functionality.

The following tasks need to be finished first, before this can be implemented: Expose IoFilterChain (#1868936), arrays as message attributes (#1747013), id domains (#1877575).

[Hanno Braun]

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Scheduled for 0.4.

[Hanno Braun]

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Haven't gotten around to do it in time for 0.4. Rescheduled for 0.5.