[Owncloud] Repeating Events Caching

[Georg Ehrke]

Hi all,
my work on repeating events caching is nearly done. 
It's currently in the branch calendar_repeat.

It caches the occurrences of repeating events.
If you have some recurring events in ownCloud starting some years ago, it can take up to several minutes to generate them.
With repeating events caching the events will be cached for the current year ± 5 years.
This will highly improve the performance of the calendar app and the loading of the occurrences will take nearly less than one second.

I would appreciate feedback and some help testing this new feature.

If no one reports huge problems until Wednesday (6/20/2012) i will merge it into master.

Cheers, 
Georg Ehrke