Allow no metadata for non-OData clients

If a client sends an Accept header requesting JSON with a specific odata.metadata level, the service responds with that level. If a client sends a request with OData-Version or OData-MaxVersion and does not specify an odata.metadata level, the service responds with odata.metadata=minimal. If a client sends a request and does not specify OData-Version or OData-MaxVersion and does not specify an odata.metadata level, the service may respond with any format matching the Accept header, e.g. for application/json any JSON dialect, including OData JSON of the odata.metadata level preferred by that service.