some script rework

One of our customers had a problem with the plugin on a Adora Belle system. My colleague @thesunrise1983 updated the plugin and moved the script to make use of jQuery.

Note: the changes also need a small core fix applied in splitbrain/dokuwiki@fc7684bc7f41c3351955f71b8a94a73bb11aa358

BTW, the plugin page should be moved ``plugin:npd`` and the reference to the old SVN repo be replaced with a link to the github repo (we missed that the first time)