Remove obsolete tests.
Use poltergeist instead of selenium
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.
Merge pull request #53 from Senjai/2-2-calcrefactor

Refactor calculator to ensure an up to date adjustment total.