feat(i18n): Add Korean translation strings

[JSYoo5B]

Information for whom can't understand Korean

• In Korean, generally there is no difference between singular and plural forms.
  (not typo for [tag]-[tags], [category]-[categories] and so on)
• To list up categories and series, It'd be better to express with colon used before list.
• It seems unnecessary to express with [includedIn] for Korean.
  It'd be explicitly derived to understand the post's categories and series info.
• Didn't translate [pageNotFound] because I guess these short sentences may be acceptable for Koreans.

한국어를 이해하는 분들을 위한 정보 (Information for whom understands Korean)

• 기존 영문의 경우 문장형으로 서술되어있으나, 그대로 번역 시 과번역되는 듯 하여, 구절 형태로 번역하였습니다.
• 테마 선택에서 적절한 번역이 없는 것 같아서, 직설적으로 "밝게, 어둡게, 검정" 으로 번역했습니다.
• Shortcodes 중 abstract는 정황 상 "추상화"보단 논문 등의 "초록"의 의미를 가지는 것 같다 생각했고,
  그보다는 "요약"이 적합한 표현이라 생각하여 이렇게 번역했습니다. (마침 summary가 따로 존재하지 않습니다.)

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