Redirect CustomTabs docs to WebFu

- Adds a JS redirect on customtabs.html
- Adds meta robots noindex to customtabs.html
- Tries to configure redirects.json to trigger server redirects.

android/customtabs.html

@@ -1,5 +1,10 @@
 {{+bindTo:partials.standard_multidevice_article}}
 
+<meta name="robots" content="noindex">
+<script>
+   window.location.replace('https://developers.google.com/web/android/custom-tabs/');
+</script>
+
 <style>
 dd { margin: 0 6px 12px 40px; }
 img.inline {

android/redirects.json

@@ -0,0 +1,4 @@
+{
+  "customtabs": "https://developers.google.com/web/android/custom-tabs/",
+  "installtohomescreen": "https://developers.google.com/web/fundamentals/app-install-banners/"
+}