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/all-template-statistics.html

@@ -6,7 +6,7 @@
 
 {% block maincolumn_content %}
   <h1 class='heading-large'>
-  	Templates used this year
+  	Templates sent this year
   </h1>
   <p>
 	1 April 2016 to date