Add download link banner to Thunderbird post-download donation page.

less/pages/thunderbird.less

@@ -1,4 +1,13 @@
 .thunderbird {
+  .download-failed {
+    text-align: center;
+    background: #fff;
+    h3 {
+      font-weight: 700;
+      font-family: "Nunito Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;
+    }  
+  }
+
   &.thank-you-page,
   &.share-page {
     display: block;

locales/en-US/messages.properties

@@ -71,6 +71,8 @@ additional_info_thunderbird=We’re the leading open source cross-platform email
 additional_info_thunderbird_2=While Thunderbird is now an independent project separate from Mozilla, Mozilla has agreed to collect donations on our behalf.
 # String only displayed on https://donate-mozilla-org-us-staging.herokuapp.com/thunderbird/?test=tbdownload
 thunderbird_thank_you_note=Thank you for downloading Thunderbird!
+# String only displayed on https://donate-mozilla-org-us-staging.herokuapp.com/thunderbird/?test=tbdownload
+thunderbird_download_banner=Your download should have begun automatically. If it didn’t work, <a href="https://www.thunderbird.net/download/">try downloading again here</a>.
 
 # Paypal donate page
 select_donation=Select your donation amount

src/pages/thunderbird/about.js

@@ -1,4 +1,5 @@
 import React from 'react';
+import { FormattedHTMLMessage } from 'react-intl';
 import ThunderbirdFooter from '../../components/thunderbird/footer.js';
 import SingleForm from '../../components/single-form.js';
 
@@ -28,13 +29,18 @@ module.exports = React.createClass({
     });
   },
   render: function() {
+    var downloadBanner = "";
     var className = "row additional-info-container thunderbird";
     if (this.props.test) {
       className += " " + this.props.test;
     }
+    if (this.props.test === "tbdownload") {
+      downloadBanner = (<div className="download-failed"><h3><FormattedHTMLMessage id="thunderbird_download_banner" /></h3></div>);
+    }
     var aboutCopy = this.state.aboutCopy;
     return (
       <div className={className}>
+        {downloadBanner}
         <div className="additional-info-page">
           <div className="container additional-page">
             <img className="internet-graphic" width="224" src="/assets/images/thunderbird/thunderbird-logo-wordmark-small.png"/>