Ensure tests don't exceed rate limit, use mock responses

[compscidr]

There are two issues here, one is that we are making real requests to scholar (which we probably still want some of, but we also want to carefully avoid throttling across multiple test runs). This may mean some local persistence of the request rate or something that can span multiple runs of the program.

The second issue is that we should probably have reproduced responses used to mock the response from the actual server side of things for the majority of tests.