[6.0] Add acceptance tests with Behat

[SammyK]

What do you guys think about adding some acceptance tests with Behat? You think it'd be useful? Then we could remove the live calls to Graph from the unit tests. :)

[yguedidi]

Tests are always great! :)
But we should not test the Graph API, only the SDK and its usage

[SammyK]

My thoughts were that Behat wouldn't be testing the Graph API, rather the SDK's interaction with the Graph API ensuring that the expected responses were being processed properly. Since the Graph API changes often (and it's not always documented!), acceptance tests would be a good automated way to ensure that the functionality in the SDK isn't broken. What do you think? :)