Core: High-Dpi progress bar

Also tweaking the ProgressBar painting code. The cancel cross was
slightly messed up lately, since line drawing changed in Qt5. The
progress bar is one pixel taller and the cancel button mouse area is
slightly larger.

Change-Id: Id55c21f45529332dc6abfc03b53f149e8349a9a0
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>

src/plugins/coreplugin/progressmanager/progressbar.h

@@ -93,6 +93,7 @@ private:
     float m_cancelButtonFader;
     bool m_finished;
     bool m_error;
+    QRect m_cancelRect;
 };
 
 } // namespace Internal