Change back "Sidebars" -> "Sidebar"

src/lib/app/mainmenu.cpp

@@ -538,7 +538,7 @@ void MainMenu::init()
 
     QMenu* toolbarsMenu = new QMenu(tr("Toolbars"));
     connect(toolbarsMenu, SIGNAL(aboutToShow()), this, SLOT(aboutToShowToolbarsMenu()));
-    QMenu* sidebarMenu = new QMenu(tr("Sidebars"));
+    QMenu* sidebarMenu = new QMenu(tr("Sidebar"));
     connect(sidebarMenu, SIGNAL(aboutToShow()), this, SLOT(aboutToShowSidebarsMenu()));
     QMenu* encodingMenu = new QMenu(tr("Character &Encoding"));
     connect(encodingMenu, SIGNAL(aboutToShow()), this, SLOT(aboutToShowEncodingMenu()));

src/lib/navigation/navigationbar.cpp

@@ -378,7 +378,7 @@ void NavigationBar::aboutToShowToolsMenu()
     m_menuTools->clear();
 
     m_window->createToolbarsMenu(m_menuTools->addMenu(tr("Toolbars")));
-    m_window->createSidebarsMenu(m_menuTools->addMenu(tr("Sidebars")));
+    m_window->createSidebarsMenu(m_menuTools->addMenu(tr("Sidebar")));
     m_menuTools->addSeparator();
 
     for (const WidgetData &data : qAsConst(m_widgets)) {