Don't use cherrypy.url to build the SVG embedded URLs
    
    cherrypy.url returns an absolute URL, not a relative one.  Pretty much
    everywhere else we deal in relative URLs, so ipsilon is generally
    friendly to being behind a reverse proxy.
    
    Merges: #155
    Signed-off-by: Howard Johnson <merlin@merlinthp.org>
    Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>