Allow creating and linking along a nullable single-valued navigation

Remove restriction on "containment" and allow PUT/PATCH if a NavigationPropertyBinding exists for the target navigation property, or the payload includes a context specifying where the new entity is to be created This affects the second paragraph of section  11.4.4 Upsert an Entity . Current text: Upserts are not supported against media entities, single-valued non-containment navigation properties, or entities whose keys values are generated by the service. Services MUST fail an update request to a URL that would identify such an entity and the entity does not yet exist. New text: Upserts to single-valued navigation properties are possible for containment navigation properties, non-containment navigation properties with a navigation property binding, or payloads including a context URL specifying the entity set or contained collection of entities in which the new entity is to be created. Upserts are not supported against media entities or entities whose keys values are generated by the service. Services MUST fail an update request to a URL that would identify such an entity and the entity does not yet exist.