for 10.8 systems, join linked contacts into 1
Various IM data fixes:

* Better contact image selection for linked contacts (10.8+)
* Properly add IM data (10.7+)
* Add data for linked people (10.8+)
* Avoid adding 'none' labels for data from IM services
Merge pull request #6 from quicksilver/pjr

linked contacts and better adding of IM/Social media info