Add Thunderbird sponsorship banner to home, uploads and download page

server/clientConstants.js

@@ -19,6 +19,7 @@ module.exports = {
     UPLOAD_AREA_NOTICE_HTML: config.upload_area_notice_html,
     UPLOADS_LIST_NOTICE_HTML: config.uploads_list_notice_html,
     DOWNLOAD_NOTICE_HTML: config.download_notice_html,
+    SHOW_THUNDERBIRD_SPONSOR: config.show_thunderbird_sponsor,
     COLORS: {
       PRIMARY: config.ui_color_primary,
       ACCENT: config.ui_color_accent

server/config.js

@@ -284,6 +284,11 @@ const conf = convict({
     default: '',
     env: 'SEND_DOWNLOAD_NOTICE_HTML'
   },
+  show_thunderbird_sponsor: {
+    format: Boolean,
+    default: false,
+    env: 'SHOW_THUNDERBIRD_SPONSOR'
+  },
   ui_color_primary: {
     format: String,
     default: '#0a84ff',