Respect game visibility

Currently, the server broadcasts all games to all players. However, games marked as PRIVATE should not be broadcasted at all and games marked as FRIENDS should only be sent to friends.

1. Remove the unused `com.faforever.server.game.GameAccess`
1. Don't serialize `visibility` when sending games to client (in `com.faforever.server.integration.legacy.transformer.GameResponsesTransformer#game`)
1. Implement a method similar to `com.faforever.server.game.GameService#markDirty` that allows specifying a list of players to send to
1. Extend `com.faforever.server.client.DelayedResponse` so that a list of receivers can be specified. The list should be nullable (so make its getter return an Optional), in which case it's considered a broadcast (document this in the getter)
1. Refactor `com.faforever.server.client.ClientService#broadcastDelayedResponses` so that it either broadcasts the response or sends it to the list of recipients.
1. Adjust and add unit tests accordingly