Make live badge cache friendly

[twschiller]

The live badge can't be used on cached views because the notification count is included in the templated HTML. To enable use with cached views, it would be helpful to have the option to:

• Do not render a count/list in the HTML returned from the server
• Cache the previously retrieved notifications client side, e.g., in local or session storage

See example implementation here: https://github.com/twschiller/open-synthesis/blob/master/assets/js/notify.js