scroll the controls panel's rows instead of clipping them

src/ui/ControlsPanel.h

@@ -10,6 +10,7 @@
 
 class GameWorldView;
 class QLabel;
+class QScrollArea;
 class QTimer;
 class QVBoxLayout;
 
@@ -64,6 +65,9 @@ private:
     const GameWorldView* m_view;
 
     QLabel*      m_heading;
+    // Scrolls the rows once they outgrow the space the panel has (REQ-UI-CONTROLS-PANEL).
+    // The heading is deliberately outside it, so it stays put and stays clickable.
+    QScrollArea* m_scrollArea;
     QWidget*     m_rows;
     QVBoxLayout* m_rowsLayout;
     QTimer*      m_refreshTimer;