Linked to MDL-10364

The idea is to have a checkbox for standardisation of grades before application of calculation.

The reason is that, for example, you may have 3 items, each of them with a very different range (0-100, 0-4, 54-4646 etc...). Applying a formula such as
=(gi1 + gi2 + gi3) / 3
is meaningless, since the item with the smallest range will drastically affect the resulting mean.

The implementation would simply standardise the grades from each included grade_item before applying the calculation. Doing this manually in the calculation would be very complex, even impossible for some teachers who may not have a great grasp of mathematics.