Add method for registering multiple audio source managers in one go

Author: devoxin

main/src/main/java/com/sedmelluq/discord/lavaplayer/player/AudioPlayerManager.java

@@ -40,6 +40,16 @@ public interface AudioPlayerManager {
      */
     void registerSourceManager(AudioSourceManager sourceManager);
 
+    /**
+     * Same as {@link #registerSourceManager(AudioSourceManager)} but registers multiple in one call.
+     * @param sourceManagers The source managers to register, which will be used for subsequent loadItem calls
+     */
+    default void registerSourceManagers(AudioSourceManager... sourceManagers) {
+        for (AudioSourceManager sourceManager : sourceManagers) {
+            registerSourceManager(sourceManager);
+        }
+    }
+
     /**
      * Shortcut for accessing a source manager of a certain class.
      *