Get checkboxes in place of per user finalization in exam mode

It should be easier to finalize some students at same time. For the moment you have to click on each student arrow to finalize them.
A multiple checkbox selection could improve the finalization mechanism.

Start by locating the exam-mode view that shows each student's finalization arrow and trace the existing per-student finalization action. Add a multiple-selection control for finalization and verify that selected students can be finalized together without changing the existing individual action.

索引モデルが issue の本文から書いたものです。