version 4.21 - js and css changes

Removed 2.0 backend_staticpage.tpl javascript to newly added staticpage_backend.js, included by this templates file.

Append renamed (style_)staticpage_backend.css to 29y backend page header. Now use of inclusion to serendipity.css, since grown a bit.

Added jquery.simplePagination.js script to use entrypaging on entrylists. This works well with some deci- pages and saves some requests. Also this avoids needing a filter function.

Top (4 option) tab bar is now concealable, since not used very often.

Minor changes, like removing "html" from Smarty escape.