Add optional submission info columns to gradesheet

The gradesheet shows student submissions for one assignment. If you click on the student name/email, you can also see some details about their submission: submission number, timestamp, grace days used, and penalty late days used. Sometimes it would be helpful to have this data available in the row data (so, you could sort, on timestamp, or submission number).

The proposal is to add a checkbox/link at the top of the screen to display this additional information in column format instead of needing to click for it.

Related: #12 (closed)