Add some max-age to device and browser icons so that they can be served directly from cache.

lib/roles/app/middleware/browser-icons.js

@@ -1,8 +1,12 @@
-var express = require('express')
+var serveStatic = require('serve-static')
 
 var pathutil = require('../../../util/pathutil')
 
 module.exports = function() {
-  return express.static(
-    pathutil.root('node_modules/stf-browser-db/dist'))
+  return serveStatic(
+    pathutil.root('node_modules/stf-browser-db/dist')
+  , {
+      maxAge: '30d'
+    }
+  )
 }