Update instagram.class.php
Update foursquare.class.php

Link to API ready for translation
Update google_plus.class.php

Added link to Googleplus Wiki page for G+ API
Update google_plus.class.php

added link to Wiki page for G+ API info.
Ready for translation.
Merge pull request #119 from danito/master

Link to api's for 4sq and Instagram ready for translation. Added link to G+ wiki page