refactor: move loadHidpiIcon from ActionManager to ToolButton.

setting loadHidpiIcon in ToolButton is better than ActionManager.
ToolButton has less code and its aim also include loading icon.

app/toolbutton.h

@@ -15,6 +15,8 @@ public:
     ToolButton(bool hoverColor = false, QWidget * parent = nullptr);
     void setIconResourcePath(const QString &iconp);
 
+    static QIcon loadHidpiIcon(const QString &resp, QSize sz = QSize(32, 32));
+
 public slots:
     void setOpacity(qreal opacity, bool animated = true);