Ajax csrftoken

These are to make it possible to use AJAX with the CSRF token even if there have been no accesses to pages with forms (ones where `{% csrf_token %}` could be used, which sets the `csrftoken` cookie).

They are possible due to a URL I've added to the site: `/csrf/`. When you request that URL, there is no content, but the application sets the `csrftoken` cookie, which is enough to make the next POST requests be issued correctly.