Add an action to show/hide the mode bar on the far left.

Change-Id: If7a74eed7fc77b1d0fd5e4045671b3767fe2d7a2
Reviewed-by: Petar Perisin <petar.perisin@gmail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
(cherry picked from commit bde0627e59)

src/plugins/coreplugin/coreconstants.h

@@ -98,6 +98,7 @@ const char EXIT[]                  = "QtCreator.Exit";
 
 const char OPTIONS[]               = "QtCreator.Options";
 const char TOGGLE_SIDEBAR[]        = "QtCreator.ToggleSidebar";
+const char TOGGLE_MODE_SELECTOR[]  = "QtCreator.ToggleModeSelector";
 const char TOGGLE_FULLSCREEN[]     = "QtCreator.ToggleFullScreen";
 
 const char MINIMIZE_WINDOW[]       = "QtCreator.MinimizeWindow";