PLT-2994 Added @all (#3233)

* Added @all

* Uncomment @all server side

webapp/components/user_settings/user_settings_notifications.jsx

@@ -842,7 +842,7 @@ class NotificationsTab extends React.Component {
                             />
                             <FormattedMessage
                                 id='user.settings.notifications.channelWide'
-                                defaultMessage='Channel-wide mentions "@channel"'
+                                defaultMessage='Channel-wide mentions "@channel", "@all"'
                             />
                         </label>
                     </div>
@@ -896,12 +896,9 @@ class NotificationsTab extends React.Component {
                 keys.push('@' + user.username);
             }
 
-            // if (this.state.allKey) {
-            //     keys.push('@all');
-            // }
-
             if (this.state.channelKey) {
                 keys.push('@channel');
+                keys.push('@all');
             }
             if (this.state.customKeys.length > 0) {
                 keys = keys.concat(this.state.customKeys.split(','));