Clarify that a server cannot support Graphson1.0 over HTTP

If a user sends an HTTP request to the server with MIME type for Graphson1.0 in the accept header, the server will always return an error, irrespective of the configured serializers. 

This is because the only serializer which support MIME type `application/vnd.gremlin-v1.0+json` is `GraphSONMessageSerializerGremlinV1d0` and it will not work with HTTP requests because it's not a `MessageTextSerializer`

We should clarify this somewhere in the docs.

Alternatively, we can support graphson v1.0 over HTTP by:
1. Register both `GraphSONMessageSerializerV1d0` and `GraphSONMessageSerializerGremlinV1d0` serializers with the server.
2. Add graphson v1.0 to supported mime types of `GraphSONMessageSerializerV1d0`
3. Change HttpEndpointHandler's chooseSerializer method to favour a MessageTextSerializer when two serializers are available for asme MIME type.

Given that graphson 1.0 is on the path to deprecation, I would suggest that we just make a change to the documentation at this stage instead of alternative option.