force all users log out when server shuts down, and force one user log out when losing connection to corresponding client
Merge branch 'dev' of https://github.com/plumer/diki into dev
Merge branch 'dev' of https://github.com/plumer/diki into dev
修复了获取单词卡结果为null的异常
不允许同一帐号多地登录；增加了服务器端的图形化显示