[form] fix #719285, due to multiple calls to restore_previous_post, by proper refactorings * move __init__ code from FieldsForm to Form. Must behaviour here should actually be in the Form base class * avoid buggy duplicated call to restore_previous_post * move some code that was in the form renderer to the form'__init__ method (__redirectpath & __form_id hidden input handling)) * 'formvid' should now be specified on form selection, not on form rendering

CubicWeb.require('ajax.js');

function removeBookmark(beid) {
    d = asyncRemoteExec('delete_bookmark', beid);
    d.addCallback(function(boxcontent) {
	    reloadComponent('bookmarks_box', '', 'boxes', 'bookmarks_box');
  	document.location.hash = '#header';
 	updateMessage(_("bookmark has been removed"));
    });
}