Facebook iOS SDK 3.7

Summary:
     see https://developers.facebook.com/ios/change-log-3.x/

    Upgrading from 3.6
     https://developers.facebook.com/docs/tutorial/iossdk/upgrading-from-3.6-to-3.7

Reviewed By: jacl

Test Plan: Release Testing.
Merge https://github.com/facebook/facebook-ios-sdk into sdk-3.5 (v3.7)