Listen for attack actions in GameBoard

[Phrancis]

While a game is being played, the game servers sends message such as the one below to signal that an action has taken place.

{
  "command":"use",
  "requestId":0,
  "id":61,
  "action":"Attack",
  "gameId":11,
  "targets":[‌​96],
  "performer":44
}

Having a listener for these messages would allow us to make a more dynamic user interface, for example animations, or a more human-friendly way to display actions as text in a chat-style dialog.