Display user dates in django admin

Refs https://redmine.teklia.com/issues/9824

We need to display the User.created & User.last_login dates in a few spots in the django admin:

• On the user details /admin/users/user/ID/change/:
  • a new fieldset with read-only User.created & User.last_login
• On the group details /admin/users/group/ID/change/
  • on the rights inline list, read-only User.created & User.last_login
  • please add a select_related to avoid making N+1 SQL queries
• On the users list /admin/users/user/
  • add the User.last_login next to created

changed milestone to %Arkindex 1.7.2

added Feature P2 labels

assigned to @mlbonhomme

changed the description

mentioned in merge request !2511 (merged)

closed