Add support for breadcrumb when offline

Currently, the main content of the page can be computed when the user has no access to the backend server.
But, this is not the case for the rest of the dynamic content. An existing element of the UI that suffer from this is the breadcrumb which will go missing when one goes offline.
But, other examples can easily be found. For instance: the list and the count of attachments.

We need to think of a better offline design allowing to easily support offline for new sources of information.