Add support for temp usernames and an interstitial to confirm username

When a user now logs in for the first time for any external auth (LDAP, JWT, Keystone, Github, Google, Dex), they will be presented with a confirmation screen that affords them the opportunity to change their Quay-assigned username.

Addresses most of the user issues around #74

data/users/federated.py

@@ -52,7 +52,8 @@ class FederatedUsers(object):
       db_user = model.user.create_federated_user(valid_username, email, self._federated_service,
                                                  username,
                                                  set_password_notification=False,
-                                                 email_required=self._requires_email)
+                                                 email_required=self._requires_email,
+                                                 confirm_username=True)
     else:
       # Update the db attributes from the federated service.
       if email: