Add NewGRF feature: Extra station name strings

These are used when all the default names have been used up,
instead of "Town Station #NNN".

src/station.cpp

@@ -38,6 +38,9 @@
 StationPool _station_pool("Station");
 INSTANTIATE_POOL_METHODS(Station)
 
+std::array<ExtraStationNameInfo, MAX_EXTRA_STATION_NAMES> _extra_station_names;
+uint _extra_station_names_used;
+
 
 StationKdtree _station_kdtree(Kdtree_StationXYFunc);
 
@@ -76,6 +79,7 @@ Station::Station(TileIndex tile) :
 	truck_station(INVALID_TILE, 0, 0),
 	ship_station(INVALID_TILE, 0, 0),
 	indtype(IT_INVALID),
+	extra_name_index(UINT16_MAX),
 	time_since_load(255),
 	time_since_unload(255),
 	station_cargo_history_cargoes(0),