Issue #91 : move user account storage from PacoClient to PacoAuthenticator
Issue #91 : move detailed log in logic from PacoMainViewController to PacoClient
Issue #91 : if a valid cookie exists, no need to log in
Issue #91 : hide loginWithClientLogin as an internal method
Issue #91 : code refactor to improve
Issue #91 : store user account inside keychain
Issue #91 : delete username and password stored in keychain when user first launch our app.
Issue #91 : set a threshold of 30 minutes for cookie's expiration interval
Issue #109 : add a category for NSError to check if the error is offline error
Issue #109 : add re-authentication process if cookie expires; avoid submitting events if user is not logged in
Issue #109 : whenever an authorization error happen, invalidate the current stored user information, and ask user to re log-in
Issue #109 : avoid re-prefetching by adding a safe-guard
Issue #109 : don't delete the account yet after authentication failed, since we may need that later
Issue #91 : add version number and attach copyright
merge ios-init
Merge pull request #154 from google/issue91

Issue #91 and Issue #109