Add usage to the dashboard

Takes the number of emails and SMS fragments sent from:
https://github.com/alphagov/notifications-api/pull/273

Using these numbers it’s possible to show:
- how much of your allowance is left
- or how much you have spent

For now the allowance and rates are hard coded.

Only for users that have manage service.

app/templates/views/dashboard/dashboard.html

@@ -6,6 +6,8 @@
 
 {% block maincolumn_content %}
 
+  <div class="dashboard">
+
     {% if not templates and current_user.has_permissions(['send_texts', 'send_emails', 'send_letters'], any_=True) %}
       {% include 'views/dashboard/get-started.html' %}
     {% elif current_user.has_permissions([
@@ -20,4 +22,6 @@
 
     {% include 'views/dashboard/today.html' %}
 
+  </div>
+
 {% endblock %}