MOBSDK-772: Fix NSInvalidArgumentException in + -[AlfrescoOAuthHelper retrieveOAuthDataForAuthorizationCode:oauthData:completionBlock:]

Also upgraded Xcode project settings, fixed warning and updated SDK references in samples apps.
Merge pull request #315 from gavincornwell/master

MOBSDK-772: Fix NSInvalidArgumentException in AlfrescoOAuthHelper