kadenz: changed adding a page number from js to css

Before the modification, the page numbers are added dynamically with js
on initialize.  The new mechanism uses counter on css.  For detailed
implementation, see themes/simple/design.css.
kadenz: fixed animation bugs

* js/kadens.js: The bugs on the element animation and page transition
are fixed.  The bug on element animation occurs as the property of the
element will not reverted on turning back a page.  Moreover the bugs on
the element animation or page transition (I don't know which caused),
but the causes might be removed.