Adds an R-key toggle that swaps supported ships between their independent/manual and Cargo Ships waterway forms.

• indep-boat <-> boat
• indep-container_cargo_ship <-> container_cargo_ship
• indep-fishing-trawler <-> fishing-trawler
• indep-battleship <-> battleship
• indep-aircraft-carrier <-> aircraft-carrier
• indep-patrol-boat <-> patrol-boat