[Assignments] Change to a group assignment after a student has submitted

[deannan_cureton]

Problem statement:

Once an assignment has been created, if your intent is to make it a group assignment, but you forget to click the box, there is no way to change it to a group submission once someone has submitted to the assignment. Please change this.

Proposed solution:

Allow submissions to be updated to group submissions even if someone has submitted the assignment.

User role(s):

instructor