Refactor calculator to ensure an up to date adjustment total.

Unfortunately, we need an up to date adjustment total to apply gift cards
correctly. This is not something the calculator knows about, as adjustments
can be added that would change the total before the totals are persisted on
the order. So we have to recalculate that total ourselves.

This also fixes some tests from a previous PR. Jenkins wasn't marking the build properly, these tests are obsolete.