[studio] fix unformatted html in connection error message (TNL-5818)

display default error message for non-json responses (TNL-5818)

[studio] log ajax errors. (TNL-5818)

[studio] fix failing test (TNL-5818)

[cms-test] avoid circular error logging; stub Logger (TNL-5818)

[cms-test] fix logger dep in squire config (TNL-5818)

[cms-tests] fix logger import (TNL-5818)

[cms-test] stub the logger directly in the karma config. (TNL-5818)

[studio] didn't need Logger after all (TNL-5818)

[studio] ignore console.log (TNL-5818)

cms/static/cms/js/main.js

@@ -25,23 +25,24 @@
                 dataType: 'json'
             });
             $(document).ajaxError(function(event, jqXHR, ajaxSettings) {
-                var message, msg;
+                var msg, contentType,
+                    message = gettext('This may be happening because of an error with our server or your internet connection. Try refreshing the page or making sure you are online.');  // eslint-disable-line max-len
                 if (ajaxSettings.notifyOnError === false) {
                     return;
                 }
-                if (jqXHR.responseText) {
-                    try {
-                        message = JSON.parse(jqXHR.responseText).error;
-                    } catch (error) {
-                        message = str.truncate(jqXHR.responseText, 300);
-                    }
-                } else {
-                    message = gettext('This may be happening because of an error with our server or your internet connection. Try refreshing the page or making sure you are online.');  // eslint-disable-line max-len
+                contentType = jqXHR.getResponseHeader('content-type');
+                if (contentType && contentType.indexOf('json') > -1 && jqXHR.responseText) {
+                    message = JSON.parse(jqXHR.responseText).error;
                 }
                 msg = new NotificationView.Error({
                     'title': gettext("Studio's having trouble saving your work"),
                     'message': message
                 });
+                console.log('Studio AJAX Error', { // eslint-disable-line no-console
+                    url: event.currentTarget.URL,
+                    response: jqXHR.responseText,
+                    status: jqXHR.status
+                });
                 return msg.show();
             });
             $.postJSON = function(url, data, callback) {