Problems 1-7

Had some trouble working out the
test_quarterly_on_second_installment_bill_date_with_full_payment test
with the problem 7 restriction (see comment at test for more
information). For problem 5 I edited some of the code under the comment
saying that that section of the program shouldn't needed to be edited,
perhaps I misunderstood the question? As that was how all the other
Policies were added I assumed that's where Policy Four needed to be
placed. Similar issue with problem 6.

I will certainly be looking over these solutions a few more times before
I submit them as finished though!