Allow omitting key properties from PUT and PATCH request bodies and from nested entities in deep-insert requests

In PUT and PATCH requests key properties can't be changed, and their immutable value can be derived from the request URL, so they MAY be omitted from the request body. In POST requests properties that are marked as "store generated", i.e. the server determines their value, MAY be omitted from the request body. In deep-insert requests the key properties of nested entities that are tied to key properties of the enclosing entity by a referential constraint MAY be omitted from the request body. Accepted: https://www.oasis-open.org/committees/download.php/48411/odata-meeting-27_on-20130228-minutes.html#odata-265