Improve default challenge loading and creating.

Remove world name from challenge and challenge level ids when default file is created.
Reassign correct world name to unique id when challenges and levels are loaded.

src/main/java/world/bentobox/challenges/ChallengesImportManager.java

@@ -245,9 +245,36 @@ private boolean loadDefaultChallenges(User user, World world)
 
         try
         {
+        	// This prefix will be used to all challenges. That is a unique way how to separate challenged for
+			// each game mode.
+			String uniqueIDPrefix = Util.getWorld(world).getName() + "_";
         	DefaultDataHolder defaultChallenges = new DefaultJSONHandler(this.addon).loadObject();
-        	defaultChallenges.getChallengeList().forEach(challenge -> manager.loadChallenge(challenge, false, user, true));
-			defaultChallenges.getLevelList().forEach(level -> manager.loadLevel(level, false, user, true));
+
+        	// All new challenges should get correct ID. So we need to map it to loaded challenges.
+        	defaultChallenges.getChallengeList().parallelStream().forEach(challenge -> {
+        		// Set correct challenge ID
+        		challenge.setUniqueId(uniqueIDPrefix + challenge.getUniqueId());
+				// Set up correct level ID if it is necessary
+        		if (!challenge.getLevel().isEmpty())
+				{
+					challenge.setLevel(uniqueIDPrefix + challenge.getLevel());
+				}
+				// Load challenge in memory
+				manager.loadChallenge(challenge, false, user, user == null);
+			});
+
+			defaultChallenges.getLevelList().parallelStream().forEach(challengeLevel -> {
+				// Set correct level ID
+				challengeLevel.setUniqueId(uniqueIDPrefix + challengeLevel.getUniqueId());
+				// Set correct world name
+				challengeLevel.setWorld(Util.getWorld(world).getName());
+				// Reset names for all challenges.
+				challengeLevel.setChallenges(challengeLevel.getChallenges().stream().
+					map(challenge -> uniqueIDPrefix + challenge).
+					collect(Collectors.toSet()));
+				// Load level in memory
+				manager.loadLevel(challengeLevel, false, user, user == null);
+			});
         }
         catch (Exception e)
         {
@@ -288,12 +315,34 @@ private void generateDefaultChallengeFile(World world)
 
 				List<Challenge> challengeList = manager.getAllChallenges(world).
 					stream().
-					map(Challenge::clone).
+					map(challenge -> {
+						// Use clone to avoid any changes in existing challenges.
+						Challenge clone = challenge.clone();
+						// Remove world name from challenge id.
+						clone.setUniqueId(challenge.getUniqueId().replaceFirst(replacementString, ""));
+						// Remove world name from level id.
+						clone.setLevel(challenge.getLevel().replaceFirst(replacementString, ""));
+
+						return clone;
+					}).
 					collect(Collectors.toList());
 
 				List<ChallengeLevel> levelList = manager.getLevels(world).
 					stream().
-					map(ChallengeLevel::clone).
+					map(challengeLevel -> {
+						// Use clone to avoid any changes in existing levels.
+						ChallengeLevel clone = challengeLevel.clone();
+						// Remove world name from level ID.
+						clone.setUniqueId(challengeLevel.getUniqueId().replaceFirst(replacementString, ""));
+						// Remove world name.
+						clone.setWorld("");
+						// Challenges must be reassign, as they also contains world name.
+						clone.setChallenges(challengeLevel.getChallenges().stream().
+							map(challenge -> challenge.replaceFirst(replacementString, "")).
+							collect(Collectors.toSet()));
+
+						return clone;
+					}).
 					collect(Collectors.toList());
 
 				DefaultDataHolder defaultChallenges = new DefaultDataHolder();