fix: avoid create menu actions everytime when trigger context menu.

fix the minor memory leak issue, also bring some possibility to
implement custom keybinding.

And oops I also did another feature in this commit..
Now we are able to set mouse wheel behavior in config dialog.

app/actionmanager.h

@@ -0,0 +1,30 @@
+#ifndef ACTIONMANAGER_H
+#define ACTIONMANAGER_H
+
+#include <QAction>
+
+class MainWindow;
+
+class ActionManager
+{
+public:
+    ActionManager();
+    ~ActionManager();
+
+    void setupAction(MainWindow * mainWindow);
+    void retranslateUi(MainWindow *MainWindow);
+    void setupShortcuts();
+
+public:
+    QAction *actionCopyPixmap;
+    QAction *actionCopyFilePath;
+    QAction *actionPaste;
+    QAction *actionToggleStayOnTop;
+    QAction *actionToggleProtectMode;
+    QAction *actionSettings;
+    QAction *actionHelp;
+    QAction *actionProperties;
+    QAction *actionQuitApp;
+};
+
+#endif // ACTIONMANAGER_H