Mail sending

* adds mail sending logic for new notification setting
* adds new templates for user and team based sending
* enhances all email template layout
* adds translations

templates/email/api/verify_token.html

@@ -6,6 +6,7 @@
     <article>
         {% trans 'Hello support' %},
         <br>
+        <br>
         {% trans 'you need to verify the API token for user' %}:
         <br>
         <br>