[nemo-qml-plugin-contacts] Make contact browsing faster

Adapt to having partial contact information in the cache until
completion is requested.  Provide more data roles from the model so
that clients do not need to instantiate a Person unnecessarily.
Update dependencies.
Qt4 fixes.
Merge pull request #28 from matthewvogt/partial-contacts

[nemo-qml-plugin-contacts] WIP - make contact browsing faster