Hide top widget and tabbar in fullscreen

This change hides the topwidget and tabbar when fullscreen shortcut/button is pressed.
If the mouse is taken to the top of screen, they are shown till the time it is there.

src/mainwindow.cpp

@@ -22,6 +22,7 @@ MainWindow::MainWindow(QWidget *parent) :
     mp_ui->tabBar->setStackedWidget(mp_ui->mainView);
 
     auto app = KiwixApp::instance();
+    addAction(KiwixApp::instance()->getAction(KiwixApp::ToggleFullscreenAction));
 
     connect(app->getAction(KiwixApp::ExitAction), &QAction::triggered,
             this, &QMainWindow::close);
@@ -75,12 +76,44 @@ MainWindow::~MainWindow()
 }
 
 void MainWindow::toggleFullScreen() {
-    if (isFullScreen())
+    if (isFullScreen()) {
+        QApplication::instance()->removeEventFilter(this);
+        showTabAndTop();
         showNormal();
-    else
+    }
+    else {
+        QApplication::instance()->installEventFilter(this);
+        hideTabAndTop();
         showFullScreen();
+    }
+}
+
+void MainWindow::hideTabAndTop() {
+    getTabBar()->hide();
+    getTopWidget()->hide();
+}
+
+void MainWindow::showTabAndTop() {
+    getTabBar()->show();
+    getTopWidget()->show();
+}
+
+bool MainWindow::eventFilter(QObject* /*object*/, QEvent* event)
+{
+    if (event->type() == QEvent::MouseMove && isFullScreen())
+    {
+        const auto mouseEvent = static_cast<QMouseEvent*>(event);
+        if (mouseEvent->y() == 0) {
+            showTabAndTop();
+        } else if(mouseEvent->y() >= 150) {
+            hideTabAndTop();
+        }
+        return true;
+    }
+    return false;
 }
 
+
 void MainWindow::when_ReadingList_toggled(bool state)
 {
     if (state) {

src/mainwindow.h

@@ -27,11 +27,14 @@ class MainWindow : public QMainWindow
 
 protected:
     void keyPressEvent(QKeyEvent *event);
+    bool eventFilter(QObject* object, QEvent* event) override;
 
 private slots:
     void toggleFullScreen();
     void when_ReadingList_toggled(bool state);
     void when_libraryPageDisplayed(bool showed);
+    void hideTabAndTop();
+    void showTabAndTop();
 
 private:
     Ui::MainWindow *mp_ui;