[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...
[caldav] Sync calendars even if they have not been previously synced for an account

Since an account has multiple calendars, the decision to choose a slow
sync versus a quick sync for a notebook should depend on whether a
notebook already exists for a particular calendar, rather than whether
the account has previously been synced.