function plugin : write the url corresponding to the given jelix action for javascript

it creates a javascript string, that contains the url, with dynamic javasript parameters
example : {urljsstring 'jxacl~admin_rightslist',array(),array('grpid'=>'idgroup','__rnd'=>'Math.random()')};
it will produce: "index.php?module=acl&action=admin_rightslist&grpid="+idgroup+"&__rnd="+ Math.random();

• jTpl $tpl: template engine
• string $selector: selector action
• array $params: parameters for the url
• array $jsparam: array : key=name of a url parameter, value=piece of javascript code ( variable name for example)
• $jsparams