♻️(models) refactor user email fields

The email field on the user is renamed to "admin_email" for clarity. The
"email" and "name" fields of user's main identity are made available on
the user model so it is easier to access it.

src/backend/demo/tests/test_commands_create_demo.py

@@ -31,3 +31,14 @@ def test_commands_create_demo():
     assert models.Identity.objects.exists()
     assert models.Team.objects.count() == 3
     assert models.TeamAccess.objects.count() >= 3
+
+
+def test_commands_createsuperuser():
+    """
+    The createsuperuser management command should create an use
+    with superuser permissions.
+    """
+
+    call_command("createsuperuser")
+
+    assert models.User.objects.count() == 1