[web] Move request handling logic into cubicweb application. (closes #2200684) We improve http status handling in the process: ``application.publish`` have been renamed to ``application.handle`` to better reflect it's roles. The request object gain a status_out attribute to convey the HTTP status of the response. WSGI and etwist code have been updated. Exception gain status attribute

/* sortable tables */

table.listing tr .headerSortUp {
  background-image: url(asc.gif);
}
table.listing tr .headerSortDown {
  background-image: url(desc.gif);
}
table.listing tr .headerSortDown, table.listing tr .headerSortUp {
   background-color: %(listingBorderColor)s;
   background-repeat: no-repeat;
   background-position: center right;
}