finished cn translations and set up multi-lang page titles

_i18n/cn.yml

_i18n/en.yml

_includes/header.html

_layouts/static_page.html

downloads/index.md

getting-started/accepting.md

getting-started/choose.md

getting-started/donate/index.md

getting-started/merchants.md

getting-started/running.md

knowledge-base/about.md

knowledge-base/developer-guides/index.md

knowledge-base/openalias.md

knowledge-base/people.md

knowledge-base/projects.md

knowledge-base/user-guides/index.md

research-lab/index.md