Support mt() Events

[hissy]

Let's make it enable to add onload & onerror events from outside of the package.

Example usage:

$app = \Concrete\Core\Support\Facade\Facade::getFacadeApplication();
$director = $app->make('director');
$director->addListener('on_before_dispatch', function () use ($app) {
    $mautic = $app->make(\Concrete\Package\Mautic\Asset\Tracker::class);
    $mautic->setParam('foo', 'bar');
    $mautic->setOnLoadFunction("alert('Tracking request is loaded');");
    $mautic->setOnErrorFunction("alert('Tracking request is error');");
});

Output:

<script>
    (function(w,d,t,u,n,a,m){w['MauticTrackingObject']=n;
        w[n]=w[n]||function(){(w[n].q=w[n].q||[]).push(arguments)},a=d.createElement(t),
        m=d.getElementsByTagName(t)[0];a.async=1;a.src=u;m.parentNode.insertBefore(a,m)
    })(window,document,'script','https://mautic.test/mtc.js','mt');
    mt('send', 'pageview', {"foo":"bar"}, {onload: function() {alert('Tracking request is loaded');},onerror: function() {alert('Tracking request is error');}});
</script>