External metadata support

[yatounoneko]

I hope to load external metadata files (e.g., .opt#1575 Mentioned in the discussion) with the same name in the same folder as the comic files (e.g., .pdf, .cbr/.cbz, .zip, .rar).

I have looked at #277 & #1240 and noticed that most PDFs contain really crappy metadata. Some PDF file from TW online comics providers also lack accurate metadata.

However, I can import these files into Calibre, edit the metadata, and then output metadata files with the same name (.opt).

So is this a feasible method? Similar to how subtitles are used as external files for videos. ( Similar to request #1713 )

[gotson]

Duplicate of #1713