Depend on newest version of libcontacts
[nemo-qml-plugin-contacts] DisplayLabel property is now cached

Now exposed from PeopleModel as 'displayLabel' rather than 'display'.
[nemo-qml-plugin-contacts] Add resetContactData function

Allows a contact to be reset back to it's original state, by refreshing
the details retrieved from the backend.
Merge pull request #37 from matthewvogt/display-label

DisplayLabel property is now cached