Subtitles with language codes & multi-episode files

Move subtitles along with video files (#66)
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Allows to keep language codes in subtitle name intact - for example 'original-name.eng.srt' is renamed to 'new-name.eng.srt'.

Better handling of multi-episode files
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There are some episodes on thetvdb.com that are part of multi-episode but don't have number in the name (for example Star Trek DS9, 1x01 'Emissary' and 1x02 'Emissary (2)'). Using previous code, the episode name would be 'Emissary, Emissary (2)'. After the change the name is correctly 'Emissary (1-2)'.