Create new user: better visibility about existing users

- Mette Zacho

In the user creation procress, we have made it more visible if a user is already created in the organization.

Today, it is not possible to invite a user into an organization if the user is created with an email that is already registered to another user in the organization.

Previously, when you wanted to create a new user, there was no visible information that the user had already been created - and might have been deactivated. 

We've fixed the issue so a message will appear if an email address already exists on a user, whether the user is active in the organization or not.