Support /agenda/(day|...)/DATE.

E.g., /agenda/day/2013-11-11 will show the agenda for <2013-11-11 Mon>.

* src/org-ehtml-server.el (org-ehtml-serve-file): Support params for
  `org-agenda-list'.

Signed-off-by: Rüdiger Sonderfeld <ruediger@c-plusplus.de>