Added abstraction layer around config.

`roles` in config renamed to `defaultRoles`. These are used if no `roles` are provided in production.yaml

client/src/Home.js

@@ -19,8 +19,8 @@ export default class List extends Component {
 
         return (
             <div>
-                <h2>{t('welcomeToMailtrain')}</h2>
-                <div>TODO: some dashboard</div>
+                <h2>{t('Mailtrain 2 beta')}</h2>
+                <div>{t('Build') + ' 2019-07-26-1703'}</div>
             </div>
         );
     }