Add `restricted` icon

src/images/icons/restricted.svg

+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><g fill-rule="evenodd"><rect fill="none" stroke="none" x="0" y="0" width="16" height="16"></rect><path fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M8 1C4.5 1 1 4.5 1 8s3.5 7 7 7 7-3.5 7-7-3.5-7-7-7zm0 7l-4 4 4-4 4-4-4 4z"></path></g></svg>

src/sidebar/components/svg-icon.js

@@ -41,6 +41,7 @@ const icons = {
   profile: require('../../images/icons/profile.svg'),
   public: require('../../images/icons/public.svg'),
   refresh: require('../../images/icons/refresh.svg'),
+  restricted: require('../../images/icons/restricted.svg'),
   reply: require('../../images/icons/reply.svg'),
   search: require('../../images/icons/search.svg'),
   share: require('../../images/icons/share.svg'),