#123 Startup sync delay to prevent duplicate entries

[Frank E.]

Add a (configurable?) startup sync delay, so Outlook can first sync calender folder with Exchange server. Or only start CalDavSync sync if connection to Exchange is already synced.

Cause: if using multiple computers, and CalDavSync is faster than sync with Exchange, you can end up with multiple version of the same calendar entry (entry is already on Exchange, because synced with second PC, than CalDavSync syncs it again, and than Outlook gets the entry a second time from Exchange sync).