Added two methods to PlayerManager

These two methods are mainly for networking. This lets you send Packets to any players 'watching' any given chunk.

Example:

    public static void sendMessageToTile(SimpleNetworkWrapper wrapper, TileEntity tileEntity, IMessage message)
    {
        if(tileEntity.getWorldObj() instanceof WorldServer)
        {
            ((WorldServer)tileEntity.getWorldObj).getPlayerManager().sendToWatching(tileEntity.xCoord >> 4, tileEntity.zCoord >> 4, wrapper.getPacketFrom(message));
        }
    }