revert: remove protected mode

protected mode is designed for borderless and transparent window.
it is not suit for the goal of this fork.

app/actionmanager.h

@@ -45,7 +45,6 @@ public:
     QAction *actionCopyFilePath;
     QAction *actionPaste;
     QAction *actionTrash;
-    QAction *actionToggleProtectMode;
     QAction *actionToggleAvoidResetTransform;
     QAction *actionSettings;
     QAction *actionHelp;