Fheroes2 scenario editor, boat suggestions

[LeHerosInconnu]

In the scenario editor:

• it should be possible to mark a boat as belonging to a player.
• a boat located in a city's ocean access square is automatically marked as belonging to the player controlling that city.
• it should be possible to place a hero directly in a boat, just like the hero in the jail (PoL).
• it should be possible to mark a neutral boat as not summonable with the Summon Boat spell.

Related discussion: #7482.