A review request without a draft that is marked as public=False would be

shown with a draft banner on RB 1.7, but the work on 2.0 broke that.

This was partially due to a change when reorganizing the

review_header.html template, and was further hindered by some missing

logic in the views.
Now, a review request created through the New Review Request page

without a draft will once again have a banner, and the Publish and

Discard buttons will work again.
It also fixes an issue with the error callback for Publish. It turns out

that it didn't have the correct parameters.

Unit tests pass.
Created an attachments-only review request and a review request from a commit.

Saw the draft banner. 
Hitting Publish also published it (if a default reviewer was set up), or gave

an appropriate error (if reviewers were blank).
Discard also worked.