Update isImage to not use jQuery

Updates #814

src/utils.js

@@ -46,11 +46,20 @@
 
     var isImage = function (url) {
         var deferred = new $.Deferred();
-        $("<img>", {
-            src: url,
-            error: deferred.reject,
-            load: deferred.resolve
-        });
+        var img = new Image();
+        var timer = window.setTimeout(function () {
+            deferred.reject();
+            img = null;
+        }, 3000);
+        img.onerror = img.onabort = function () {
+            clearTimeout(timer);
+            deferred.reject();
+        };
+        img.onload = function () {
+            clearTimeout(timer);
+            deferred.resolve(img);
+        };
+        img.src = url;
         return deferred.promise();
     };
 
@@ -86,12 +95,12 @@
                 }
                 $obj.html(x);
                 _.forEach(list, function (url) {
-                    isImage(url).then(function (ev) {
+                    isImage(url).then(function (img) {
                         var prot = url.indexOf('http://') === 0 || url.indexOf('https://') === 0 ? '' : 'http://';
                         var escaped_url = encodeURI(decodeURI(url)).replace(/[!'()]/g, escape).replace(/\*/g, "%2A");
                         var new_url = '<a target="_blank" rel="noopener" href="' + prot + escaped_url + '">'+ url + '</a>';
-                        ev.target.className = 'chat-image';
-                        x = x.replace(new_url, ev.target.outerHTML);
+                        img.className = 'chat-image';
+                        x = x.replace(new_url, img.outerHTML);
                         $obj.throttledHTML(x);
                     });
                 });