Add /_stats endpoint

Also, remove ingest_stats worker and use the cache instead.

client/About.js

@@ -1,8 +1,7 @@
 import React from 'react'
 import contentHTML from './About.md'
 
-function About() {
-  return <div className="wrapper" dangerouslySetInnerHTML={{ __html: contentHTML }}/>
-}
+const About = () =>
+  <div className="wrapper" dangerouslySetInnerHTML={{ __html: contentHTML }}/>
 
 export default About