User list should use first name as secondary sort key

For example our 3 Dohertys should appear in the order Gavin, Kevin and Stephen. Applies to Labjam user list and to the A-Z on the public website.

You also need some 3rd level sort key for such cases as Ian O'Keefee (we've 2 in the database) to keep a stable order. This could just be the internal ID.