Update Japanese translation

[ryonakano]

• Review and modify fuzzy translations
• Improve readability and consistency of existing translations
• Do not translate proper nouns (human names, Jorts the app name, Pantheon, elementary OS, etc.)
• Remove translations for release notes
  • Sorry, I feel the current translations are sounds weird for me a native speaker of Japanese, but it's hard for me to review and keep them up to date. So I think we should remove them rather than keeping incomplete translations
• Purge orphan translations

[teamcons]

  * Sorry, I feel the current translations are sounds weird for me a native speaker of Japanese, but it's hard for me to review and keep them up to date. So I think we should remove them rather than keeping incomplete translations

Please do not apologize. We value your judgment, and for japanese you know better, so whatever your decisions we follow

Thank you very much for your work on the translations. It is really appreciated. We are proud of this little app, and the languages are very much a part we cannot improve much on for other languages than ours. So this is really amazing :)