Makes the 'listUsers' function users 'List.Controller' run as callback in the fetch success function

This ensures that the ui elements are only put into DOM when all the
data to be viewed in them as been fetched
Adds 'List.Empty' view for users when the collection is empty
Creates the 'LeadsApp' along with its corresponding controller, view and template

Can be tested by manually navigating to /#leads in the browser