Merge pull request #477 from khawkins/unstable

Mobile SDK: Merging master into unstable
OAuth should not mess with the shared webview cache
Merge pull request #478 from khawkins/no_webiew_cache_actions

OAuth should not mess with the shared webview cache
Adding abstractions to the creation, presentation, and dismissal of passcode screens
Merge pull request #484 from khawkins/passcode_updates

Adding abstractions to the creation, presentation, and dismissal of passcode screens