Merge pull request #1634 from chibicode/gh-pages

[Translations: /ja] Japanese translation
Minor update to wording

Document refers to a different file than the one the user has been shown to download.
Merge pull request #1682 from mfeckie/patch-2

Minor update to wording
Translate mail/index.md
Translate usage/index.md
Translate ja/usage/faq.md
Translate ja/usage/configuration.md
Translate ja/usage/settings.md
Translate ja/usage/managing.md
Translate ja/usage/writing.md
Minor tweaks for usage/*.md
Translate themes/index.md except one section
Translate themes/index.md
Typo fixes
More typo fixes
Merge branch 'gh-pages' of https://github.com/chibicode/Ghost into gh-pages

# By Shu Uesugi (7) and Yasuharu Sawada (5)
* 'gh-pages' of https://github.com/chibicode/Ghost:
  More typo fixes
  Typo fixes
  Translate themes/index.md
  Translate themes/index.md except one section
  Minor tweaks for usage/*.md
  Translate ja/usage/writing.md
  Translate ja/usage/managing.md
  Translate ja/usage/settings.md
  Translate ja/usage/configuration.md
  Translate ja/usage/faq.md
  Translate usage/index.md
  Translate mail/index.md