Allowing ids to be mutated by admins from the /internal/config pages is dangerous.
This could cause issues if an admin tries to update the SiteConfig.staff_user_id to an id that is another user's id, or to an id that isn't valid.
* Add rate_limit_follow_count_daily to SiteConfig
* Add favicon_url to SiteConfig
* Add logo_svg to SiteConfig
* Add staff_user_id to SiteConfig
* Add default_site_email to SiteConfig
* Add social_networks_handle to SiteConfig
* Add ga_view_id and ga_fetch_rate to SiteConfig
* Add mailchimp newsletters IDs to SiteConfig
* Add periodic_email_digest_max, periodic_email_digest_min to SiteConfig
* Redirect /internal to /internal/articles avoiding annoying 404
* Set the navbar on two rows
* Add :main_social_image to SiteConfig and to the internal view
* Add simple tests
* Ameliorate the UI
