Assert a maximum number of SQL queries on API view request tests

[CloudNiner]

Follow up to #523, we should ensure that other views aren't exhibiting the same behavior by including a check against the number of sql queries ran for each API view test.

[rmartz]

Django's assertNumQueries will be what we want, it can be used as a wrapper for a code block:

with self.assertNumQueries(2):
    Person.objects.create(name="Aaron")
    Person.objects.create(name="Daniel")