Use a layout definition for displaying metadata on the lightbox view

This view is already generated using JavaScript. It could be the occasion to test a light approach with fetching a layout definition for rendering some data in JavaScript. That way, the view will be configurable via Nuxeo Studio.

An endpoint already exists for fetching the useful information (http://localhost:8080/nuxeo/site/layout-manager/ , must be moved to new /config endpoint)

• A limited set of widgets should be defined/reviewed (date, vocabulary, string, list ? ...)
• Mapping of Nuxeo widgets to that set should be completed
• a simple to integrate library of javascript widgets to use by default should be evaluated (even if in this specific use case, we just need to display read only data...
• a documentation page on the approach has to be produced