Exam bank: Bulk actions - frontend

[some-molasses]

We should allow admins to bulk hide and delete exams.

We would probably need:

• A way to "select" exams - consider a checkbox on the left side of each exam item
• A display near the top of the table saying "n exams selected"
• A "clear selection" button
• "Hide all" and "delete all" buttons. Let's consider putting these in a dropdown called "actions", that is only clickable when items are selected, and is otherwise greyed out.