the ajax-processes can now be canceled

when the user clicks on the button the ajax-process is started and the
text of the button is prefixed with "Cancel ". now, when the user clicks
on the button again, the ajax-process is aborted and the text is
changing back to the old value.
i streamlined the javascript-implementation to reduce the
per-mod-generated javascript and the javascript code inside the
mod.class.php. currently i have no idea how to get the wordpress-i18n
into the admin_ajax-javascript.