Add ".default" to the name of downloaded subtitles

Hey, I think this would be a great feature for Bazarr if there is the support and time to add it. Adding ".default" to the name of the subtitles before ".srt" would make Emby treat the subtitles downloaded through Bazarr as the default subtitles when playing something with subtitles enabled. This would be a killer feature because it would make all my Movies and TV shows with subtitles default to the srt subtitles as opposed to embedded subtitles that require transcoding.

More on Emby subtitle naming conventions here https://github.com/MediaBrowser/Wiki/wiki/Subtitles