starting porting away from KCal::Calendar: add copies of KCal::Calendar and KCal::CalenderNull to KOrganizer and use them instead of the KCal versions, so we can refactor them towards the interface we want.
Disables quite some features relying on KCal classes (IncidenceFormatter, MailScheduler, for example), which should be changed to not take a Calendar* where possible.

svn path=/branches/work/akonadi-ports/kdepim/; revision=1031925