错误：
RuntimeError: Model class user.models.UserAccount doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS.
解决方案：
方案一、删除关于模型层from xxx import UserAccount的引用（不推荐此方法）
方案二、
检查注册app的settings文件，是否是这样注册的：'apps.user'（apps为装app文件夹）
检查你引用UserAccount的地方，是否这样引用：from apps.user.models import UserAccount
检查urls.py的引用是否是这样引用：apps.user.urls
若还有错误继续检查有引用模型文件夹下.py文件的地方，
把 user 的引用改为 apps.user 的引用
将
from xxx.apps.users.models import User
改为
from users.models import User
原因网址：
原因：
Django's Sites Framework is a contributed module bundled with the core library that allows for the use of a single Django application/codebase with different sites (that can use different databases, logic in views, etc). The SITE_ID setting, as stated in the docs, "is used so that application data can hook into specific sites and a single database can manage content for multiple sites."
In this particular case AllAuth requires the Sites Framework in order to function properly. Many other third-party libraries are built to safely handle cases where multiple sites may be present and as such may be best .
