[Qt] Raise debug window when requested

* Raise the debug window when hidden behind other windows
* Switch to the debug window when on another virtual desktop
* Show the debug window when minimized

This change is a conceptual copy of 5ffaaba and 382e9e2

src/qt/bitcoingui.h

@@ -191,6 +191,8 @@ private Q_SLOTS:
     void optionsClicked();
     /** Show about dialog */
     void aboutClicked();
+    /** Show debug window */
+    void showDebugWindow();
     /** Show help message dialog */
     void showHelpMessageClicked();
 #ifndef Q_OS_MAC