Add support for Peregrine's Sling Model based on JSon Schemas

[schaefa]

We have JSon Schema supported in the Object Definitions. Now we need to support them in Sling Models to make the visible.
An object based on an object definition should show the properties provided by the object definition in their model view (object-name.model.json).
Add support for nested reference schemas and cache schemas but check for updates.

[schaefa]

I added the changes to the Object Model into a new branch: issues/1011-add-json-schema-support-to-sling-models