Ensure consistency between extension-categories, between torrent-player and torrent-poster.

Add additional audio-file-extensions.

src/renderer/lib/media-extensions.js

@@ -0,0 +1,8 @@
+const mediaExtensions = {
+  audio: ['.aac', '.asf', '.flac', '.m2a', '.m4a', '.m4b', '.mp2', '.mp4', '.mp3', '.oga', '.ogg',
+    '.opus', '.wma', '.wav', '.wv', '.wvp'],
+  video: ['.avi', '.mp4', '.m4v', '.webm', '.mov', '.mkv', 'mpg', 'mpeg', '.ogv', '.webm', '.wmv'],
+  image: ['.gif', '.jpg', '.jpeg', '.png']
+}
+
+module.exports = mediaExtensions