Add vcr for youtube test

[rtibbles]

Summary

• Adds the VCR library for testing
• Monkey patches to fix an extant issue in the library when kwargs are passed to the urllib3 response read method
• Moves all test requires specification into setup.py for ease of installation
• Turns the VCR use_cassette decorator instead into a pytest.mark.skip if vcr is unavailable (we can't install it on Python 3.9 as it requires an incompatible version of urllib3 there)

References

This will allow us to test that #573 doesn't break Youtube downloading
Also will allow for testing of future GDrive integration

Reviewer guidance

Is this adequately documented?
Are tests passing?