Add a common base email template, translate the emails over to using jinja and add emails when e-mail addresses and passwords are changed.

emails/paymentfailure.html

@@ -0,0 +1,13 @@
+{% extends "base.html" %}
+
+{% block content %}
+
+<h3>Subscription Payment Failure</h3>
+
+Your recent payment for account {{ username | user_reference }} failed, which usually results in our payments processor canceling
+your subscription automatically. If you would like to continue to use {{ app_title }} without interruption,
+please add a new card to {{ app_title }} and re-subscribe to your plan.<br>
+<br>
+You can find the card and subscription management features under your {{ username | admin_reference }}<br>
+
+{% endblock %}