Provide "next/prev/back to the list" links on a document when selecting it from search results

The page provider API already has a notion of "current entry" so that's not the issue.

Problems are:

• there can be several content views on a page => need to find a way to set and retrieve the "current content view" used to generate prev/next/back to the list links, and also to generate the "back to the list" link as the content view has currently no knowledge of the page displaying it

• setting the current entry on the page provider should be handled by the url system transparently (to set it when clicking on a item of the list), but it could be costly to retrieve the "current content view" and set it as the current entry on every navigation