[ProgressBar] Use update() instead of repaint()

update() does not trigger repaint immediately. It helps with
speed of restoring crashed session (progressbar does not need to be
refreshed for every restored tab immediately).

The same change was made for SiteIcon in PopupLocationBar

src/lib/popupwindow/popuplocationbar.cpp

@@ -34,7 +34,7 @@ public:
     explicit PopupSiteIcon(QWidget* parent = 0) : QWidget(parent) { }
     void setIcon(const QIcon &icon) {
         m_icon = QIcon(icon.pixmap(16, 16));
-        repaint();
+        update();
     }
 
 private:

src/lib/tools/progressbar.cpp

@@ -33,7 +33,7 @@ void ProgressBar::setValue(int value)
 {
     m_value = value;
     if (m_lastPaintedValue != m_value) {
-        repaint();
+        update();
     }
 }