Disable nukes option (#237)

This makes it possible to disable all nukes as well as missile silos
from the game in privat lobbies and singleplayer games

src/server/GameManager.ts

@@ -34,6 +34,7 @@ export class GameManager {
       gameType: GameType.Private,
       difficulty: Difficulty.Medium,
       disableNPCs: false,
+      disableNukes: false,
       infiniteGold: false,
       infiniteTroops: false,
       instantBuild: false,