mcrypt is deprecated in PHP >= 7.1

I’m testing with PHP7.1 and have been getting deprecation warnings. Sure they can be silenced, but it’s probably best to look at this issue sooner rather than later as mcrypt will be removed sometime soon. I’ts used at least here: https://github.com/minimus/sam-pro-free-public/blob/master/sam-pro-front.php#L206