后端：用户登录、退出登录、获取用户状态相关功能完成；引入SessionManager；数据库：user_identity改为group；前端：添加登录页面、后台管理页面框架，axios POST请求Content-Type问题修复，引入md5、sha1 js库；小问题调整

bookshelfplus/src/main/java/plus/bookshelf/Service/Impl/UserServiceImpl.java

@@ -30,7 +30,7 @@ public class UserServiceImpl implements UserService {
         userModel.setUsername(userDO.getUsername());
         userModel.setEncriptPwd(userDO.getEncriptPwd());
         userModel.setNickname(userDO.getNickname());
-        userModel.setUserIdentity(userDO.getUserIdentity());
+        userModel.setGroup(userDO.getGroup());
         userModel.setAvatar(userDO.getAvatar());
         userModel.setPhone(userDO.getPhone());
         userModel.setWeixinThirdPartyAuthCode(userDO.getWeixinThirdPartyAuthCode());