Make the monthly Usage details page consistent.

Move the "excess usage from previous month" line in the monthly Usage Detail page from the "This month" section into the "Allowance calculation" section. Having last months over use included in this months total makes a nonsense of *This* months total.

Carried forward under use *is* displayed in the Allowance calculation section, meaning the page presents different totals depending on over/under use the previous month. With under use the "Units in the month" total is just "units in the month". With over use the "Units in the month" is inflated by the *previous* months over use. And the useful "Total allowance in this month" line is missing.