Add "opus" and "mka" extension to default

This add 2 more extensions to the default scanned audio files. see #603 for more details

airsonic-main/src/main/java/org/airsonic/player/service/SettingsService.java

@@ -133,7 +133,7 @@ public class SettingsService {
     private static final String DEFAULT_IGNORED_ARTICLES = "The El La Los Las Le Les";
     private static final String DEFAULT_SHORTCUTS = "New Incoming Podcast";
     private static final String DEFAULT_PLAYLIST_FOLDER = Util.getDefaultPlaylistFolder();
-    private static final String DEFAULT_MUSIC_FILE_TYPES = "mp3 ogg oga aac m4a flac wav wma aif aiff ape mpc shn";
+    private static final String DEFAULT_MUSIC_FILE_TYPES = "mp3 ogg oga aac m4a flac wav wma aif aiff ape mpc shn mka opus";
     private static final String DEFAULT_VIDEO_FILE_TYPES = "flv avi mpg mpeg mp4 m4v mkv mov wmv ogv divx m2ts";
     private static final String DEFAULT_COVER_ART_FILE_TYPES = "cover.jpg cover.png cover.gif folder.jpg jpg jpeg gif png";
     private static final int DEFAULT_COVER_ART_CONCURRENCY = 4;