Make it possible to find transfer user by email

The Vue Multiselect uses one prop for the local search. Although the API
already returned matching users for a given email, the users were
filtered out as their displayname doesn't contain the search string –
the email address.

Disabling the local seach and only using the most recently fetched
matches fixes this problem.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>