Subtitle encoding normalization (to utf8)

[robfrawley]

Add support for subtitle encoding normalization by detecting file encoding using file -i input.ext to detect current encoding and iconv -f format -t UTF-8//TRANSLIT input.ext output.ext to re-encode as utf-8. See the following resources for additional implementation information:

• https://www.tecmint.com/convert-files-to-utf-8-encoding-in-linux/