Loading map from server

[sashman]

• Commit a generated map from server.
• Include terrain sprite sheet and json describing it.
• TerrainRequester class:
  • Sends request to server to fetch all maps.
  • Load map json info into Terrain class.
  • Use the socket to send request.
  • Handler for receiving terrain.
• Server side request handler for requesting terrain by map.
• Terrain events handled by ClientGameInitialiser