Use multiselection

autotests/groupmanagementwidgettest.cpp

@@ -40,4 +40,5 @@ void GroupManagementWidgetTest::shouldHaveDefaultValues()
 
     auto mListView = w.findChild<QListView *>(QStringLiteral("mListView"));
     QVERIFY(mListView);
+    QCOMPARE(mListView->selectionMode(), QAbstractItemView::MultiSelection);
 }

src/groupmanagementwidget.cpp

@@ -32,6 +32,7 @@ GroupManagementWidget::GroupManagementWidget(QWidget *parent)
 
     mListView->setObjectName(QStringLiteral("mListView"));
     mainLayout->addWidget(mListView);
+    mListView->setSelectionMode(QAbstractItemView::MultiSelection);
     init();
 }