#21 Add tagging support for internal/external subtitles

Just like the Full HD, 5.1 logos and such, add support for some kind of subtitles logos too.

Subtitles can either be internal (in .mkv files mostly) or external (in .srt, .sub, .ssa, etc... formats) and they need to have the same name as the video file as you probably are aware.

My suggestion is to add support for both. This would need 3 logos:
- Internal subtitles included
- External subtitles included
- Both internal and external subtitles included

In my case, sometimes I download some movies with internal subtitles (it's not my choice) and sometimes, they already have my language, sometimes they don't. When they don't, I need to get the subtitles in my own language and that becomes the external subtitles.