dashboard: add expiration warning notification's template

circle/dashboard/templates/dashboard/notifications/vm-expiring.html

+{%load i18n%}
+{%blocktrans with instance=instance.name url=instance.get_absolute_url suspend=instance.time_of_suspend delete=instance.time_of_delete %}
+Your instance <a href="{{url}}">{{instance}}</a> is going to expire.
+It will be suspended at {{suspend}} and destroyed at {{delete}}.
+{%endblocktrans%} 
+
+{%blocktrans with token=token url=instance.get_absolute_url %}
+Please, either <a href="{{token}}">renew</a> or <a href="{{url}}">destroy</a>
+it now.
+{%endblocktrans%}