Add Italian translation.
Translate `it/installation/index.md`.
Translate `it/installations/mac.md`.
Translate `it/usage/configuration.md`.
Translate `it/usage/index.md`.
Translate `it/usage/settings.md`.
Translate `it/installation/upgrading.md`.
Merge branch 'gh-pages' of https://github.com/TryGhost/Ghost into gh-pages

Conflicts:
	_config.yml
Merge some work by @riccardobevilacqua (Thanks a lot!).
Update windows.md

Translate into italian! =)
Update linux.md

Translated into italian =)
Update managing.md

Translated into Italian! =)
Update faq.md

Translated into Italian =)
Update faq.md
Update index.md

Translated into italian!!! =)
Update index.md

Translated into Italian! =)
Improve translations a bit.
Merge branch 'gh-pages' of https://github.com/TryGhost/Ghost into gh-pages

Conflicts:
	_config.yml
Update `deploy.md` to latest changes.
Temporarily revert `mail` and `themes` tranlations.