users: upper-case email causes issues with user profile

[cenouralm]

The issue was moved from the Zenodo board.

Steps to reproduce:

1. Go to Zenodo (or an Invenio instance) without being logged-in
2. Sign up and put any part of the email address in upper-case letters (e.g. SOME@example.com)
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 some@zenodo.org is already associated with an account (see screenshot)

[ppanero]

@cenouralm Unless I'm wrong, email addresses are not case sensitive (i.e. gmail, mailchimp do not accept diff addresses with only capital diffs). I'm not sure this applies.

[lnielsen]

I think the problem here is that it behaves as if it was case-sensitive. With the nickname we store a case preserving field, and a lowercase version of the nick name......I think something similar has to happen for the email, or make sure it's always stored lowered cased.