Merge pull request #62 from baasbox/0.8.4

update from origin 0.8.4
fixes #506 GET /users?fields=user.name returns error 500
Social Mock Service refactoring...
Better management of some users' attributes

The id of social networks now are in the visiblyByRegisteredUsers._social data structure
The data collected from the social networks are stored in the visibleByTheUser field
Merge branch 'facebook_bugs' into 0.8.4
Merge pull request #509 from giastfader/0.8.4

fixes #506 and #508