Extend Order::flags to 16 bits, fixes conditional order target field size

Adjust order packing and CmdInsertOrder

See: #198

src/saveload/extended_ver_sl.cpp

@@ -135,6 +135,7 @@ const SlxiSubChunkInfo _sl_xv_sub_chunk_infos[] = {
 	{ XSLFI_LOCAL_COMPANY,          XSCF_IGNORABLE_ALL,       1,   1, "local_company",             saveLC,  loadLC,  nullptr        },
 	{ XSLFI_THROUGH_TRAIN_DEPOT,    XSCF_NULL,                1,   1, "drive_through_train_depot", nullptr, nullptr, nullptr        },
 	{ XSLFI_MORE_VEHICLE_ORDERS,    XSCF_NULL,                1,   1, "more_veh_orders",           nullptr, nullptr, nullptr        },
+	{ XSLFI_ORDER_FLAGS_EXTRA,      XSCF_NULL,                1,   1, "order_flags_extra",         nullptr, nullptr, nullptr        },
 	{ XSLFI_NULL, XSCF_NULL, 0, 0, nullptr, nullptr, nullptr, nullptr },// This is the end marker
 };