When activity is graded with a scale the values in gradebook are wrong (and different from what it was with Sum of grades).

At the same time not everything on master branch looks great as well, so I'm going to create behat tests with partial validation.

For example, if assignment is graded with a scale, the grade item percentage is displayed wrong (for the "B" on "A,B,C,D,F" scale it displays 75% instead of 80%).