Support document load listener (e.g. for URL generation)

[dantleech]

Support document load event.

Use case

Document URL generators listen to a massive_search.document_post_load event (for example) and can do things such as setting the URL for a document after it has been loaded from the search index.

There would be two:

• StaticRouteUrlDocumentListener: Generate routes using the Symfony routing system (e.g. for products)
  • Will need some sort of class map in configuration, and maybe something to do with the ExpressionLangugae to map properties to route parameters (??)
  • Or we could create a decorator per class
• StructureRouteUrlDocumentListener: Set the URL for the search result based on the current portal, etc.
• SymfonyCmfRoutingDocumentListener: Set the URL based on classes that implement the CMF RouteReferrersInterface for example..