ensure accountStore requestAccessToAccountsWithType:options:completion: callback runs in main queue
added -[STTwitterOAuth postReverseOAuthTokenRequest:errorBlock:] to perform the first step of Reverse Auth https://dev.twitter.com/docs/ios/using-reverse-auth
return non JSON response in completion block instead of error block, needed for step 2 of Reverse Auth
use a single, persisting ACAccountStore instance, as stated in https://dev.twitter.com/docs/ios/using-reverse-auth
fixed error messages
made -oauthAccessToken and -oauthAccessTokenSecret mandatory in STTwitterProtocol because STTwitterOS will know them after Reverse Auth https://dev.twitter.com/docs/ios/using-reverse-auth
added support for reverse authentication