Allow exchanging a station's name with another station in the same town

src/command_type.h

@@ -362,6 +362,7 @@ enum Commands {
 	CMD_RENAME_PRESIDENT,             ///< change the president name
 	CMD_RENAME_STATION,               ///< rename a station
 	CMD_RENAME_DEPOT,                 ///< rename a depot
+	CMD_EXCHANGE_STATION_NAMES,       ///< exchange station names
 	CMD_SET_STATION_CARGO_ALLOWED_SUPPLY, ///< set station cargo allowed supply
 
 	CMD_PLACE_SIGN,                   ///< place a sign