autocomplete: Filter user-autocomplete results according to email match, not just name

[chrisbobbe]

Currently, typing @cbobbe in the compose box gives no user-mention autocomplete results, even though my user's email address starts with cbobbe. We should include a user in the results if the query matches the user's email address.

[Khader-1]

We should show the email in the popup as well, at least when the user's email matches the query but the name doesn't