Merge pull request #42 from pvuorela/master

[nemo-qml-plugin-calendar] expose attendee information on event query
Remove unnecessary method
Remove unused recurrence exception list
[nemo-qml-plugin-calendar] separate event modifications to different class

Spreading modifications to all event instances before saving doesn't
make much sense and was just complicating things.

Created CalendarEventModification to gather bunch of changes which
can be then atomically saved.

Should also help when making changes to recurring event exceptions
for which the normal event class wouldn't fit well.