Overhaul all tests and remove cache

- Rename /test/data to /test/fixtures
- Remove unused fixtures and MockTransporter
- Mock all network requests (no external network required)
- Remove cache.js and replace with simple in-memory cache
- Add a couple media upload tests
- Add path parameter tests
- General cleanup of unused variables in all tests
Continuation lines would be good to have for nocking. Long nocks are not readable at all.
~~~ js
nock('https://www.googleapis.com')
    .post('/upload/drive/v2/files?uploadType=multipart')
    .reply(200, { fileId: 'abc123' });
~~~