Handle text based media type responses.

[darrelmiller]

If the response is text/html or text/csv, for example, we should ensure the user can access the response payload easily.

Response type in the RequestBuilder method should probably be Stream so that we can handle large responses.
AB#10130

[baywet]

For this one the plan is that anything that's not text/plain, text/xml, text/yaml, application/xml, application/json or anything that doesn't have a schema will be treated as stream. The only exception being text/plain without schema will be treated as string.
I'm going to tackle this together with #546

[baywet]

fixed via #1471