fixed crash when application haven't access to the contacts
Merge branch 'sdk1.3' of https://github.com/Sitecore/sitecore-ios-sdk into sdk1.3
[appledoc] Fixed grammar errors. Expanded some unclear comments.
[appledoc] Added class description
Merge remote-tracking branch 'origin/sdk1.3' into sdk2.0
[appledoc] Fixed session object description