Facebook: Added "email" property to class FacebookMeResponse

The FacebookMeResponse class didn't expose the email of the user. The class also didn't follow a consistent structure by exposing the internal JsonObject (most of the Facebook implementation has the same problem).

Besides the "email" property, the response from Facebook also has some other properties currently not supported by Skybrud.Social, so this is something that I'll have to look into before the next release.