[caldav] Retry initial REPORT request if it failed with QNetworkReply::AuthenticationRequiredError.

Yahoo server sometimes fails with this response even when the username
and password are sent, so do one retry if this happens. (Cannot
reproduce this problem with other tested servers.)
[caldav] Set default profile sync schedule to sync every 12 hours
Merge pull request #12 from nemomobile/retry-report

[caldav] Retry initial REPORT request if it failed with QNetworkReply::A...