View Gradesheet should show grading outputs in large text box

[TheodorJ]

Currently, the text box for Assessment -> Grade Submissions can be resized, but does not indicate such and is very small by default. We should show a larger text box for feedback.

[damianhxy]

It appears that an indicator has been added. To make the text box larger, modify min-height of #grades td .score_details .feedback in gradesheet.css.scss.

However, given that we're shifting away from the gradesheet, this issue will likely be closed as a won't fix in the near future