Inconsistent email case-sensitivity

[slint]

Describe the bug

The case-sensitivity of the email field is inconsistent throughout the sign-up, login, and settings pages.

Steps to Reproduce

1. Go to an Invenio instance without being logged-in
2. Sign up and put any part of the email address in upper-case letters (e.g. [email protected])
3. After that go to the user profile account settings page and try to change your username or full name
4. An error is returned saying [email protected] is already associated with an account.

This is probably because the email address is looked-up or compared in a case-sensitive fashion.

Expected behavior

The common consensus is that email addresses SHOULD be treated as case-insensitive. There are two approaches on this:

• Convert and store all email address input to lowercase
• Store the original user input email address but use case-insensitive methods for lookups (e.g. a lower-case column index)

Screenshots (if applicable)