CHintBox: add possibility to left hintbox with RC_up and RC_down

RC_up and RC_down are used for text scroll, but most message texts
are small and no scroll mode is required. In case of large texts
it should falling back to scroll mode.

src/gui/widget/hintbox.h

@@ -60,6 +60,7 @@ class CHintBox : public CComponentsWindow
 		int y_hint_obj;
 		int h_hint_obj;
 		int w_indentation;
+		bool enable_txt_scroll;
 
 		Font* hb_font;