Change vehicle route overlay settings

Add a mode setting: off, all locations, station stops only
Change show vehicle route setting to on/off
Move settings to their own section in the GUI
Add an unset hotkey to switch the mode setting

src/viewport_func.h

@@ -46,6 +46,7 @@ void MarkViewportLineDirty(Viewport * const vp, const Point from_pt, const Point
 void MarkTileLineDirty(const TileIndex from_tile, const TileIndex to_tile, ViewportMarkDirtyFlags flags);
 void MarkAllRoutePathsDirty(const Vehicle *veh);
 void CheckMarkDirtyFocusedRoutePaths(const Vehicle *veh);
+void CheckMarkDirtyFocusedRoutePaths();
 
 bool DoZoomInOutWindow(ZoomStateChange how, Window *w);
 void ZoomInOrOutToCursorWindow(bool in, Window * w);