fix(content-server): Move serveStatic middleware after wildcard route

Because:
* The MIME type was a mismatch for JS and CSS files without the static directory being set before the wildcard settings route

This commit:
* Ensures the serveStatic middleware comes after the wildcard route in production

packages/fxa-content-server/server/bin/fxa-content-server.js

@@ -189,19 +189,8 @@ function makeApp() {
   const routeLogger = loggerFactory('server.routes');
   const routeHelpers = routing(app, routeLogger);
 
-  if (config.get('env') === 'production') {
-    app.get(settingsPath, modifySettingsStatic);
-
-    addAllReactRoutesConditionally(app, routeHelpers, modifySettingsStatic);
-  }
-
-  if (config.get('env') === 'development') {
-    app.use(settingsPath, createSettingsProxy);
-
-    addAllReactRoutesConditionally(app, routeHelpers, createSettingsProxy);
-  } else {
-    app.get(settingsPath + '/*', modifySettingsStatic);
-  }
+  function addNonSettingsRoutes(middleware) {
+    addAllReactRoutesConditionally(app, routeHelpers, middleware);
 
     /* This creates `app.whatever('/path' ...` handlers for every content-server route and
      * excludes routes in `react-app.js` if corresponding feature flags are on. We manually add
@@ -211,12 +200,27 @@ function makeApp() {
      * route implementations. */
     routes.forEach(routeHelpers.addRoute);
 
-  // must come after route handling
+    // must come after route handling but before wildcard routes
     app.use(
       serveStatic(STATIC_DIRECTORY, {
         maxAge: config.get('static_max_age'),
       })
     );
+  }
+
+  if (config.get('env') === 'production') {
+    app.get(settingsPath, modifySettingsStatic);
+
+    addNonSettingsRoutes(modifySettingsStatic);
+
+    app.get(settingsPath + '/*', modifySettingsStatic);
+  }
+
+  if (config.get('env') === 'development') {
+    app.use(settingsPath, createSettingsProxy);
+
+    addNonSettingsRoutes(createSettingsProxy);
+  }
 
   // it's a four-oh-four not found.
   app.use(fourOhFour);