The HttpRecorder did not correctly play back binary content.  The propsed fix is to introduce
new fields in `RecordEntry` named `IsRequestBodyBinary`/`IsResponseBodyBinary`, and use base64
encoding/decoding when the payload is deemed to be binary.  Currently the test for binary-ness
is a simple MIME type regex match.

Note that this PR includes tests to confirm the new behavior.  It will failed to build without
hacking around the fact that the test code depends on the NuGet-installed Microsoft.Azure.Test.HttpRecorder.dll.
If it is preferable to split the PR so you can update NuGet first without the tests failing, please
let me know.

Test images for forthcoming tests.  Checking in first so they can be reference via URL via githubusercontent.

Generated from [PR](Azure/azure-rest-api-specs#3145).

Tests covering all the API methods.

Go back to the old HttpRecorder for now.  Thumbnail tests are commented out until
it is fixed.