Sendy's app.php page polls server too often

[dennisgorelik]

"Recent campaigns" page in Sendy (https://github.com/slim2000/sendy/blob/0ba57725da87504e2cf08b1f34f4f18716f961b6/app.php) constantly updates "percentage number of emails sent" by calling /app/progress.php page.

That causes our server's overload.
I think this line is responsible:

refresh_interval = setInterval(function(){get_sent_count('.$id.')}, 2000);

I think the interval should be higher than 2000 ms.
I recommend to set it to 30000 ms, or make it configurable.