sso: Use Login and Logout view classes instead of methods

Created by: SunilMohanAdapa

Complexity: 2 point

Django 1.11 introduced classes for Login and Logout views and deprecated the old login() and logout() method views. See release notes. Single sign on module uses these two older methods. Move to using classes instead. This can be done by either keeping our own login/logout methods or by changing our methods also into classes. Latter is better. Override the auth module's Login/Logout classes to create our own Login/Logout views and use these. Override appropriate methods to do our customization on top.