Sort preview plugins case-insensitively

"eBook thumbnails" would show up all the way at the bottom otherwise

Test Plan: 18.12 branch It now shows where it should

Differential Revision: https://phabricator.kde.org/D18787

src/settings/general/previewssettingspage.cpp

@@ -61,6 +61,7 @@ PreviewsSettingsPage::PreviewsSettingsPage(QWidget* parent) :
     QSortFilterProxyModel* proxyModel = new QSortFilterProxyModel(this);
     proxyModel->setSourceModel(serviceModel);
     proxyModel->setSortRole(Qt::DisplayRole);
+    proxyModel->setSortCaseSensitivity(Qt::CaseInsensitive);
 
     m_listView->setModel(proxyModel);
     m_listView->setItemDelegate(delegate);