Use individual directly

This removes most of the Contact class and makes use of the Individual of folks directly. The aim of this refactor is to make the code more readable. Since Individual provides most of the needed features the Contact class adds a complicated abstraction without any real benefit.

Transform FakePersona a real Persona which can be used as a placeholder till folks returns the real Persona.

Use SearchQuery to find the best matching contact when opening gnome-contacts with a e-mail address