[nemo-qml-plugin-calendar] Fix setting invalid end date to recurrence

KCalCore gets confused when setting invalid end date. On such, there
remains occurrences infinitely, but Recurrence::recursAt(),
getNextDateTime() don't work properly anymore.
Merge pull request #45 from pvuorela/recur_end_date

[nemo-qml-plugin-calendar] Fix setting invalid end date to recurrence
[nemo-qml-plugin-calendar] Support recurrence exceptions and recurrence ids

- Added recurrenceId to api
- Removed EventOccurrence:remove(), more consistent when one interface
is used for removals
- Added support for creating recurrence exceptions via EventModification
- Added support for removing all instances of an event