Issue #160: Provide Async Error Handling

Added Toast notification for unexpected errors
    On 401 and 403 Errors, user is redirected to login

webgoat-container/src/main/resources/static/js/goatApp/support/goatAsyncErrorHandler.js

@@ -0,0 +1,34 @@
+define(
+    ['backbone', 'underscore'],
+    function(Backbone, _) {
+        return {
+            init: function() {
+                var backboneSync = Backbone.sync;
+
+                var asyncErrorHandler = function(error) {
+                    return function(jqXHR) {
+                        var statusCode = jqXHR.status;
+                        var errorCodes = {
+                            404: true,
+                            500: true,
+                            503: true,
+                            504: true
+                        };
+
+                        if (statusCode === 401 || statusCode === 403) {
+                            window.top.location.href = "login";
+                        } else if(errorCodes[statusCode]) {
+                            Backbone.trigger("error:unhandled");
+                        }
+                    };
+                };
+
+                Backbone.sync = function(method, model, options) {
+                    // override error handler
+                    options.error = asyncErrorHandler(options.error);
+                    return backboneSync(method, model, options);
+                }
+            }
+        };
+    }
+);