Feature: Group liveries, and livery window usability enhancements. (#7108)

* Change: Replace checkbox in livery selection window with Default option in drop down selection.

This reduces clutter in the UI and allows for primary/secondary colours to independently follow the default scheme if desired.

* Feature: Add vehicle group liveries.

src/settings.cpp

@@ -1095,7 +1095,7 @@ static bool InvalidateNewGRFChangeWindows(int32 p1)
 
 static bool InvalidateCompanyLiveryWindow(int32 p1)
 {
-	InvalidateWindowClassesData(WC_COMPANY_COLOUR);
+	InvalidateWindowClassesData(WC_COMPANY_COLOUR, -1);
 	return RedrawScreen(p1);
 }