NemoCalendarManager does signal changed default notebooks, what does this commit mean?

Changing the default notebook makesNemoCalendarWorker to save the database, which  will cause it to reload notebooks. The reloaded notebook data will be handled by NemoCalendarManager::notebooksChangedSlot(...) [1], which will emit notebooksChanged()/defaultNotebookChanged/notebookColorChanged.

NemoCalendarNotebookModel resets its model when it gets the NemoCalendarManager::notebooksAboutToChange + NemoCalendarManager::notebooksChanged signals.

[1] https://github.com/nemomobile/nemo-qml-plugin-calendar/blob/master/src/calendarmanager.cpp#L689