Clean up ffprobe error reporting

The error messages were a bit difficult for users to understand due to a
combination of including useless technical information and lacking
userful user information.  The error messages are more verbose now and
give a better indication of what went wrong.

www/js/util.js

@@ -2070,7 +2070,7 @@ function queueMessage(data, type) {
     }
     var newAlert = makeAlert(title, text, type)
         .addClass("linewrap qfalert qf-" + type)
-        .appendTo($("#queuefail"));
+        .prependTo($("#queuefail"));
     newAlert.find(".alert").data("reason", data.msg);
 }