JSONField(binary=True) represents using binary strings, which JSONRenderer does not support. #4187

Refs #4185.

Under Python 3 the JSONField(binary=True) option is not useful because it produces bytestring output, that JSONRenderer doesn't support. We should either:

• Handle binary strings in JSONRenderer as if they by utf-8 decoding them to unicode.
• Output unicode from JSONField(binary=True) instead of a bytestring.