- Add code for placing the features information on the frontend

- Add a Features service for examining feature flags on the frontend
- Add a directive (quay-requires) that matches feature flags and, if any one does not match, removes the element from the DOM
- Add a directive (quay-show) that injects the features into the scope so that expressions of the form "Features.BILLING || something" work out of the box to show/hide the element
- Add a directive (quay-classes) that allows for setting of CSS classes on an element based on feature expression(s) such as {"!BILLING": "active"} (e.g. the BILLING flag is set to false, add the class "active".

templates/base.html

@@ -73,6 +73,7 @@
 
     <script type="text/javascript">
       window.__endpoints = {{ route_data|safe }}.apis;
+      window.__features = {{ feature_set|safe }};
       window.__token = '{{ csrf_token() }}';
     </script>