Fix difference in translation strings regarding the new Between Two Seas map (#416)

##Description:
I renamed all instances of "TwoSeas" to "BetweenTwoSeas". That way it
lowers the confusion but more importrantly - it removes the difference
between the translation strings for the map.

Please put your Discord username so you can be contacted if a bug or
regression is found:

<Nikola123>

src/core/game/TerrainMapFileLoader.ts

@@ -39,7 +39,7 @@ const MAP_FILE_NAMES: Record<GameMapType, string> = {
   [GameMapType.Australia]: "Australia",
   [GameMapType.Iceland]: "Iceland",
   [GameMapType.Japan]: "Japan",
-  [GameMapType.TwoSeas]: "TwoSeas",
+  [GameMapType.BetweenTwoSeas]: "BetweenTwoSeas",
   [GameMapType.KnownWorld]: "KnownWorld",
 };