[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
use recurrence id when saving an event
Signal event change after occurrence change has happened

Avoid warnings in case property is binding to both properties.
[nemo-qml-plugin-calendar] Provide occurrence exception state information

When creating an exception to recurring event, there might be need
to know the recurrence id of the exception.
This commit provides the value by returning a change object, which
signals finishing and provides uid+recurrence id.
Add recurrence id to warnings
Take recurrence id into account on event query refresh
Add unit test for recurrence exception modifications
Merge pull request #44 from pvuorela/master

Support recurrence id to distinguish events with same uid