Various improvements and fixes (#309)

* Remove roadmap header
* Add hostname to poweredby url
* Fix oauth button click style
* Fix mailer astuto logo
* Fix asset urls in public html files

app/javascript/components/common/PoweredByLink.tsx

@@ -3,7 +3,7 @@ import I18n from 'i18n-js';
 
 const PoweredByLink = () => (
   <div className="poweredBy">
-    <a href="http://astuto.io/?utm_campaign=poweredby" target="_blank">
+    <a href={`http://astuto.io/?utm_campaign=poweredby&utm_source=${window.location.hostname}`} target="_blank">
       { I18n.t('common.powered_by') } Astuto
     </a>
   </div>