Add "presentation mode"

Presentation mode can be entered by passing -presentationMode when
starting Qt Creator.

It displays a popup with the keyboard shortcut of the commands
that are triggered. Great for the DevDays;-)

Change-Id: I897966aab491f98e2a5abc4433c40b04e2a8db57
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>
Reviewed-by: Liang Qi <liang.qi@nokia.com>

src/plugins/coreplugin/mainwindow.h

@@ -125,6 +125,9 @@ public:
 
     void setOverrideColor(const QColor &color);
 
+    bool isPresentationModeEnabled();
+    void setPresentationModeEnabled(bool);
+
 signals:
     void windowActivated();