i18n: consolidate context for "Comment" string as just noun and verb to streamline translations.

See http://[private link]

Fixes #6552

Merges r104231-wpcom.
JSON API: Approve an unapproved comment when you reply to it.

This behavior now matches the core wp-admin/ behavior.

http://[private link]

Merges r104232-wpcom.
Merge branch 'master' of sandbox:~/jetpack