websocket
1.遍历设备
{
    "function" : "list_device",
    "messge_id": "31415"
}

成功返回示例：
{"ret":0, "func":"list_device", "message_id":"31415", "devlist":["iSlim 2000AF V2","PDS3000"]}

2.打开指定摄像头
{
    "function" : "open",
    "messge_id": "31415",
    "params": 
    {
        "device_name":"PDS3000"
    }
}

3.关闭摄像头
{
    "function" : "close",
    "messge_id": "31415"
}

