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/server/MapPlaylist.ts

@@ -88,7 +88,7 @@ export class MapPlaylist {
           Pangaea: 1,
           Asia: 1,
           Mars: 1,
-          TwoSeas: 3,
+          BetweenTwoSeas: 3,
           Japan: 3,
           BlackSea: 1,
         };