[TIMOB-19901] iOS: Expose Social and Accounts Frameworks

Sharing is such a basic feature of any app, still we don't expose the iOS [Social](https://developer.apple.com/library/prerelease/ios/documentation/Social/Reference/Social_Framework/index.html) and [Accounts](https://developer.apple.com/library/prerelease/ios/documentation/Accounts/Reference/AccountsFrameworkRef/index.html) frameworks. Many use [~viezel] his [TiSocial.Framework module](https://github.com/viezel/TiSocial.Framework/blob/master/Classes/DkNappSocialModule.m), but since it's such a basic feature we should get this into core, as discussed in the SE Flow: https://www.flowdock.com/app/appcelerator/solution-engineering/threads/LZHsYSpFhuaNNzLOQwU3ENReouA /cc [~bgrantges@appcelerator.com] [~cbowley] [~rblalock] [~matthewcongrove]