REST API: Sync posts and pages with non public post stati.

+Jetpack Options: Add 'sync_non_public_post_stati'.
Sync json_api_full_management and sync_non_public_post_stati options.
Log important settings changes.
Merge pull request #1336 from Automattic/allow-non-public-sync

Sync Posts and Pages with non-public post stati if the user opted in.