New feature: Adding some tag (enum/constant) for submit.points to determine whether points were set by a human or a autograder

[david-jezek]

This allow better control about points and distinguish points from teacher/human or autograder and alternatively allow mark points as freezed or finally assigned.

Adding another column to table submit with enum values (my favorite choice). And add code for option to autograder to overwrite only points set by autograder and not override points set by teacher.

Add code to visualize in UI source of points techar, autograder or alternatively freezwed/locked.