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/main/views/dashboard.py

@@ -80,6 +80,16 @@ def template_history(service_id):
     )
 
 
+@main.route("/services/<service_id>/usage")
+@login_required
+@user_has_permissions('manage_settings', admin_override=True)
+def usage(service_id):
+    return render_template(
+        'views/usage.html',
+        **get_dashboard_statistics_for_service(service_id)
+    )
+
+
 def add_rates_to(delivery_statistics):
 
     keys = [
@@ -148,11 +158,25 @@ def aggregate_usage(template_statistics):
 
 
 def get_dashboard_statistics_for_service(service_id):
+
+    usage = service_api_client.get_service_usage(service_id)
+    sms_free_allowance = 250000
+    sms_rate = 0.018
+
+    sms_sent = usage['data'].get('sms_count', 0)
+    emails_sent = usage['data'].get('email_count', 0)
+
     return {
         'statistics': add_rates_to(
             statistics_api_client.get_statistics_for_service(service_id, limit_days=7)['data']
         ),
         'template_statistics': aggregate_usage(
             template_statistics_client.get_template_statistics_for_service(service_id, limit_days=7)
-        )
+        ),
+        'emails_sent': emails_sent,
+        'sms_free_allowance': sms_free_allowance,
+        'sms_sent': sms_sent,
+        'sms_allowance_remaining': max(0, (sms_free_allowance - sms_sent)),
+        'sms_chargeable': max(0, sms_sent - sms_free_allowance),
+        'sms_rate': sms_rate,
     }