[WIP] Move unrelated editor cover code to the right place

Closes #4106, Closes #4103

- Moves the `.editor-close` styles to `post-settings-menu.scss`
- Renames everything that was `right-outlet` to `settings-menu`
Oh I see - I didn't know you could do that with &'s - it's slightly counter-intuitive, but I get where you were going with it now.

Now I understand the context though, it could make sense to leave it in this file. Because it is overriding default settings-menu component based on the notification component being present.