Rework Ghost Ship dungeon entrance

[mike8699]

The mechanics around the spawning of the ghost ship dungeon need to be reworked.

• When all three spirits are obtained, the ghost ship must spawn in the NW sea
• When the ghost ship boss is defeated, it must not disappear like in the vanilla game
• Somehow we need to handle the distinction between the final boss entrance and the regular ghost ship entrance.

[lunarsoap5]

iirc, the final boss ghost ship is actually in the SW sea so that shouldn't (hopefully) be too much of an issue.