Handle multiple worlds in "world" placeholder

Plugin/src/main/java/com/gmail/filoghost/holographicdisplays/placeholder/PlaceholdersManager.java

@@ -156,10 +156,27 @@ public class PlaceholdersManager {
 				worldsOnlinePlayersReplacers = new HashMap<>();
 			}
 							
-			final String worldName = extractArgumentFromPlaceholder(matcher);
-			worldsOnlinePlayersReplacers.put(matcher.group(), () -> {
-				return WorldPlayerCounterTask.getCount(worldName);
-			});
+			final String worldsNames = extractArgumentFromPlaceholder(matcher);
+			
+			if (worldsNames.contains(",")) {
+				
+				String[] split = worldsNames.split(",");
+				for (int i = 0; i < split.length; i++) {
+					split[i] = split[i].trim();
+				}
+				
+				final String[] worldsToTrack = split;
+			
+				// Add it to tracked worlds.
+				worldsOnlinePlayersReplacers.put(matcher.group(), () -> {
+					return WorldPlayerCounterTask.getCount(worldsToTrack);
+				});
+			} else {
+				// Normal, single tracked world.
+				worldsOnlinePlayersReplacers.put(matcher.group(), () -> {
+					return WorldPlayerCounterTask.getCount(worldsNames);
+				});
+			}
 		}
 		
 		// BungeeCord online pattern.

Plugin/src/main/java/com/gmail/filoghost/holographicdisplays/task/WorldPlayerCounterTask.java

@@ -43,8 +43,22 @@ public class WorldPlayerCounterTask implements Runnable {
 		}
 	}
 	
-	public static String getCount(String world) {
-		Integer count = worlds.get(world);
-		return count != null ? count.toString() : "[World \"" + world + "\" not found]";
+	public static String getCount(String[] worldsNames) {
+		int total = 0;
+		for (String worldName : worldsNames) {
+			Integer count = worlds.get(worldName);
+			if (count == null) {
+				return "[World \"" + worldName + "\" not found]";
+			}
+			
+			total += count;
+		}
+		
+		return String.valueOf(total);
+	}
+	
+	public static String getCount(String worldName) {
+		Integer count = worlds.get(worldName);
+		return count != null ? count.toString() : "[World \"" + worldName + "\" not found]";
 	}
 }