login logic
Merge branch 'master' of https://github.com/CloudEDU/CloudEDUClient

Conflicts:
	CloudEDU/CloudEDU/App.xaml.cs
右上角的用户头像 自定义 UserProfileButton 控件并数据绑定到 Constants 类中的 User 类 User 实例。User 实例在登录成功时被初始化。放弃使用 CUSTOMER 实体类，因为不易扩展。
Merge branch 'master' of https://github.com/CloudEDU/CloudEDUClient

Conflicts:
	CloudEDU/CloudEDU/Common/Constants.cs
	CloudEDU/CloudEDU/Login/Login.xaml.cs
	CloudEDU/CloudEDU/Service References/Service/Reference.cs
	CloudEDU/CloudEDU/Service References/Service/service.edmx