Object panel should not hide objects with no non-shadowed own properties

When an object has no own properties (e.g. after it has been subject of `$.user.destroy`) it is displayed by the object panel in a way that makes it look like the own properties of its prototype are actually the object's own own properties.

Similarly, if an entry in the prototype chain has no non-shadowed own properties it is omitted entirely. There should be some visual indication that there is an (effectively) empty prototype object.

(Tangentially: might we want to show shadowed properties, but perhaps greyed out?)