Initial implementation of NewGRF custom signal styles

src/newgrf_extension.h

@@ -35,6 +35,9 @@ enum Action0RemapPropertyIds {
 	A0RPI_SIGNALS_ENABLE_RESTRICTED_SIGNALS,
 	A0RPI_SIGNALS_ENABLE_SIGNAL_RECOLOUR,
 	A0RPI_SIGNALS_EXTRA_ASPECTS,
+	A0RPI_SIGNALS_NO_DEFAULT_STYLE,
+	A0RPI_SIGNALS_DEFINE_STYLE,
+	A0RPI_SIGNALS_STYLE_NAME,
 	A0RPI_OBJECT_USE_LAND_GROUND,
 	A0RPI_OBJECT_EDGE_FOUNDATION_MODE,
 	A0RPI_OBJECT_FLOOD_RESISTANT,
@@ -66,6 +69,7 @@ enum Action2VariableRemapIds {
 	A2VRI_RAILTYPE_SIGNAL_CONTEXT,
 	A2VRI_SIGNALS_SIGNAL_RESTRICTION_INFO,
 	A2VRI_SIGNALS_SIGNAL_CONTEXT,
+	A2VRI_SIGNALS_SIGNAL_STYLE,
 };
 
 /** Action14 feature definition */