Remember expanded status of tree view in statistics main window
Summary:
The collapsed tree view items of LessonStatisticsView were saved in
parleys config file. With this stored lesson names the expanded status
of the tree items will be restored when StatisticsMainWindow is
displayed next time.
Reviewers: KDE Edu, aacid
Reviewed By: aacid
Subscribers: aacid
Tags: KDE Edu
Differential Revision: https://phabricator.kde.org/D9931