Write a method called switchPairs that switches the order of values in
the list in a pairwise fashion. Your method should switch the order of
the first two values, then switch the order of the next two, switch the
order of the next two, and so on. If the list contains an odd number of
values, the final element is not moved. For example, if the list initially
stores [10, 25, 31, 47, 52, 68, 77], your method should switch the
first pair (10 and 25), the second pair (31 and 47), and the third pair (52
and 68) to yield [25, 10, 47, 31, 68, 52, 77].