Integration Casdoor SSO login

[gtn1024]

I introduced Casdoor SSO login to DWSurvey.

To use built-in login type, we can set dwsurvey.oauth.type to built-in, which is by default. To use Casdoor login type, set dwsurvey.oauth.type to casdoor and set casdoor configuration.

It did not discard the built-in login system. When logging in with Casdoor for the first time, it will create a user, email for the username and casdoor_user for the password. So it is easy to use back to the built-in login system.

Front-end code: https://github.com/wkeyuan/DWSurvey_Vue/pull/1

[nomeguy]

@wkeyuan

[easyandeasy]

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