To prevent creating multiple users with the same email via API, we should check for an existing user with given email.
Change-Id: Ie35b85c4f94a7ca72d42951dab8ff475d7f0dd7c
Currently a customer created via the IP does not get an payment account until he signs in.
That causes issues if the account should be deleted again.
Change-Id: I393c8f301e426301bb713c423d6ce011138d4ae4