Add go to depot and sell vehicle orders

Controlled by a setting (default off)

src/saveload/extended_ver_sl.cpp

@@ -86,6 +86,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_ORDER_EXTRA_DATA,       XSCF_NULL,                1,   1, "order_extra_data",          NULL, NULL, NULL        },
 	{ XSLFI_WHOLE_MAP_CHUNK,        XSCF_NULL,                1,   1, "whole_map_chunk",           NULL, NULL, "WMAP"      },
 	{ XSLFI_ST_LAST_VEH_TYPE,       XSCF_NULL,                1,   1, "station_last_veh_type",     NULL, NULL, NULL        },
+	{ XSLFI_SELL_AT_DEPOT_ORDER,    XSCF_NULL,                1,   1, "sell_at_depot_order",       NULL, NULL, NULL        },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, NULL, NULL, NULL, NULL },// This is the end marker
 };