CSS fix for 404 pages

Before, CSS would not display correctly on 404 pages, since it used a relative ``@root_path`` ``@variable``, which would give the relative url from a non-existent directory (which sometimes would lead to missing css). I've worked around this in the templates, so that CSS displays properly when you 404 on a directory that is not exactly level above your home directory (ie. yourwebsite.com/some/non/existent/directory/), which uses ``@base_url`` and ``@permalink`` instead.

Perhaps a cleaner solution can be created by modifying the behavior of ``@variables`` when encountering a 404 error instead.