Better commenting UX

Supercedes !461 (closed), closes #326 (closed).

This contains everything in !461 (closed) except for the tree structure UI.

• Comment button both at top and bottom. Bottom one is subtle and only shows if there are >0 comments,
• Show more comments button appears as a comment box, so it's more obvious
• Save buttons moved to far right as the main action button. Delete Draft colours more subtle.
• Editor shadows removed since they often caused "double-shadow"