Add a Locked attribute to exam versions, to prevent inadvertent editing of in-use versions

[blerner]

Colleague professors might want to see the exam, but not want to accidentally edit it. Add a "Confirm you really mean to edit this!" button to the current overview of the exam.

Also, add an easier way to expand all the rubrics for a print-preview version (again, so colleagues can see it more easily)

[blerner]

1-click rubric preview addressed by d283ce4