Depends on D19661. Ref T13077. See PHI840.
When a user edits a page normally, add a "Save as Draft" button. Much of this change is around making that button render and behave properly: it needs to be an `<input type="submit" ...>` so browsers submit it and we can figure out which button the user clicked.
Then there are a few minor rules:
- If you're editing a page which is already a draft, we only give you "Save as Draft". This makes edits to update/revise a draft more natural.
- Highlight "Publish" if it's a likely action that you might want to take.
Internally, there are two types of edits.
- A "content" edit changes the content //and// bumps the version.
- A "draft" edit changes the content but does not bump the version.