[Feature] IMAP user accounts are created with email address set

[almereyda]

Is your feature request related to a problem? Please describe.

When logging in with and implicitly creating a user by IMAP credentials, one has to manually add the email address to the account.

Describe the solution you'd like
If a newly created user from an IMAP user backend is created, the email address used for authenticating against the IMAP services is used to fill the email field of said user.

Describe alternatives you've considered
Administrators can go through the list of users once in a while and add these addresses by hand.

Additional context

Both users were created via IMAP login, with hof being blank and new, and my account jon being edited manually to carry the address used for login.

[almereyda]

Duplicate of #12.