Add option to add SDH/hearing impaired tag

[Firestorm2359]

Hi, love the app! It's changed the way I manage subtitles in my media server.

By default for English tracks, the automatic tag that is added to the newly created file is ".eng." This is fine however Plex will read the tag as non-hearing impaired.

Could you please consider adding an option to select whether the track is SDH or non-SDH?