Set default folders where music files can be stored

Let's use the correct default folders that RetroPie uses.

Author: bluestang2006

es-core/src/AudioManager.cpp

@@ -156,7 +156,7 @@ void AudioManager::playRandomMusic(bool continueIfPlaying)
 
 	// check in system sound directory
 	if(musics.empty())
-		getMusicIn("/usr/share/RetroPie/music", musics);
+		getMusicIn("/opt/retropie/music", musics);
 
 	// check in .emulationstation/music directory
 	if(musics.empty())
@@ -281,4 +281,4 @@ void AudioManager::update(int deltaTime)
 		Mix_VolumeMusic((int)sInstance->mMusicVolume);
 	}
 	*/
-}
+}