修改保存用户聊天数据
增加断开服务器连接功能，群消息记录功能及程序退出清楚记录文件功能，完善了客户端UDP通信(局域网)
Merge branch 'master' of https://github.com/lijianping/NetworkChat

Conflicts:
	networkchar/networkchat_client/networkchat_client/chat.cpp
	networkchar/networkchat_client/networkchat_client/main.cpp
	networkchar/networkchat_client/networkchat_client/my_socket.cpp
	networkchar/networkchat_client/networkchat_client/my_socket.h
	networkchar/networkchat_client/networkchat_client/networkchat_client.aps