Improve Chinese (Simplified) Translations (#6024)

Improve Chinese (Simplified) Translations (#6024)

* i18n: (zh-CN) Change `工作人员` (staff) to `管理人员`
Suggested by @Gargron at https://github.com/tootsuite/mastodon/pull/6005#discussion_r156678109

* i18n: (zh-CN) Change `协管` to `监察员`

* i18n: (zh-CN) Fix all "Are you" questions

* i18n: (zh-CN) Various improvements

* i18n: (zh-CN) Final clean-up

* i18n: (zh-CN) Change translation for 500

* i18n: (zh-CN) Remove spaces between time distances

* i18n: (zh-CN) Improve translations