Define and handle properly nested entities

[bolerio]

So we have this simple but effective way of managing "business entities" in the HGDB mJson module: there is a pluggable entity management interface that is capable of recognizing when a JSON object is an entity and we can tell the module to store the HGHandle in some property.

Now when an entity refers to another, we have nesting. We want the client side to be able to have the full object, perhaps even as a cyclical graph. So we need a proper convention for that so that users know how to refer to entities in JSON object properties. Or in arrays for that matter. Essentially, we need a convention whereby a JSON value represents a reference to another JSON. A bit like a URL, but we need a way to recognize that the value is a reference. And ideally it should be without too much boilerplate, without something as bloated as a context in JsonLD etc.