Added support for LinkedIn Joint Member Identification Program

The linkedIn api supports a call to query the existence of linkedIn membership based on the linkedIn email address.  This functionality is only enabled for those business partners that have a joint agreement with linkedIn and will otherwise treat all calls to this API as unauthorized.  This functionality was in the open API until November 4th 2013 but was removed.

This pull request contains test data and hooks necessary to integrate with this piece of functionality.