Parent model shall be available to JS Model script

When Java model is executed, it receives containing component's model instance.

This is essential for pages that have collaborating elements: e.g. blog post page would load pot content and add post's name to <title> element.

But post details rendering is performed by a nested content element, which would assume it is positioned in a Blog Post page and take content data from Page's model.

But in JS Model "parent" parameter is not available.

JavascriptRenderingModel constructor receives RenderingModel<?> parent parameter, but doesn't pass it to JS engine.