Add a method that creates a Bookmark for a ViewFactory, given arguments for that View.

Sometimes it may be preferable to create a Bookmark from a ViewFactory without having to incur the performance overhead of creating the actual View first. It will be handy to have a method to call.

Perhaps ViewFactory.as_bookmark can be augmented with a kwarg that prevents it from first creating the view and rather use ViewFactory.get_relative_path() to construct the relative_path for the Bookmark. In this case, description would be required and no checking would be done (at the time of Bookmark creation) whether parameterised views actually exist.