Bug 1714082: prevent users from emails being case sensitive.

All emails are checked case-insensitively, but are kept in the db in
the way user has typed
- institution regisistrations are pending and don't appear in usr,
  artefact, or artefact_internal_profile_email, but in usr_registration
  so added additonal check
- placed helper function inside user.php
- putting in a special character before the @ will give single error
- putting in a special char after the @ will flag a spam checker and out
  two errors

behatnotneeded

Change-Id: Iac1b740bc34878978ccf207d241f2399d7641040