JB Workaround CalDAV-Sync

Invalid date

The workaround now disables itself for a couple of seconds after booting the device. That ensures the original sync app can take over the account.

- new in 1.4
Change disable/enable sequence
Allow workaround to be called from CalDAV-Sync. I hope that fixes all issues with removed accounts.
On shutdown the app ensures the workaround is enabled on the next start (hence the new permission)