removed EC_toplevel, replaced references to it with ec.rational_elliptic_curves
Work on elliptic curve /Q URLs:

  Curve URLs are of the form EllipticCurve/Q/11/a/1

  Class URLs are of the form EllipticCurve/Q/11/a

  A URL of the form are EllipticCurve/Q/11 gives a list of all curves
   of conductor N

  URLs of the form EllipticCurve/Q/11.a or EllipticCurve/Q/11.a1 still
  work, via a redirect so that the page displayed has a standard URL.

  Additionally, some tidying of the curve and class web pages,
  reworking of their breadcrumbs to be consistent with the URLs, and a
  few necessary changes to links to these pages from L-function pages.