All specs - Review uses of the term "JSON object"

[Michael Jones]

Make sure that we aren't using "JSON object" anyplace where we need to actually refer to the "string representing a JSON object". This only matters if we will be base64url encoding the string.

Also look for places we say that a JSON object must be returned, but a JWT or other types are actually legal.

[Nat Sakimura]

Done. Good.