show the available controls in a panel over the world

src/ui/MainWindow.h

@@ -29,6 +29,7 @@ class Simulation;
 class GameWorldView;
 class HeaderBar;
 class SelectionPanel;
+class ControlsPanel;
 class BuildButtonBar;
 class BlueprintLibrary;
 class BuildingIconCache;
@@ -99,6 +100,7 @@ private:
     GameWorldView*         m_gameWorldView;
     HeaderBar*             m_headerBar;
     SelectionPanel*        m_selectionPanel;
+    ControlsPanel*         m_controlsPanel;
     BuildButtonBar*        m_buildButtonBar;
     // The saved blueprints themselves; they have no widget of their own any more and
     // are reached through the two modal dialogs (REQ-UI-BLUEPRINT-DIALOG).