Extract user utility code into own module

This provides more room for expansion, and reduces the amount of
arbitrary code in the __init__.py file for the new package.

app/main/views/user_profile.py

@@ -27,7 +27,7 @@ from app.main.forms import (
     TwoFactorForm,
 )
 from app.models.user import User
-from app.utils import (
+from app.utils.user import (
     user_is_gov_user,
     user_is_logged_in,
     user_is_platform_admin,