Protect NemoCalendarWorker::setDefaultNotebook() against null
[nemo-qml-plugin-calendar] Introduce notebook query class

Fetches information about notebook based on uid.
[nemo-qml-plugin-calendar] Add property for default notebook uid in calendar api
Remove change signals that happen before changes
Merge pull request #33 from pvuorela/notebookquery

Added notebook query and interfaces for default notebook
[nemo-qml-plugin-calendar] Allow querying events by uid only
[nemo-qml-plugin-calendar] Verify data in event query

Verify that event data in NemoCalendarEventQuery is valid before
emitting change signals. If event data is not valid, then there's
no point in trying to fetch occurrence data either.