Make dashboard stats update dynamically

https://www.pivotaltracker.com/story/show/115874485

This uses the same component as on the jobs page to make a partial
section of the page update itself periodically.

app/main/views/dashboard.py

@@ -1,7 +1,8 @@
 from flask import (
     render_template,
     session,
-    flash
+    flash,
+    jsonify
 )
 
 from flask_login import login_required
@@ -41,6 +42,20 @@ def service_dashboard(service_id):
         service_id=str(service_id))
 
 
+@main.route("/services/<service_id>/dashboard.json")
+@login_required
+def service_dashboard_updates(service_id):
+
+    statistics = statistics_api_client.get_statistics_for_service(service_id)['data']
+
+    return jsonify(**{
+        'today': render_template(
+            'views/dashboard/today.html',
+            statistics=expand_statistics(statistics),
+        )
+    })
+
+
 def expand_statistics(statistics, danger_zone=25):
 
     if not statistics or not statistics[0]: