show list of nodes without report for x hours in overview

- the amount of hours is defined as `UNRESPONSIVE_HOURS` in default_settings.py
- small status layout improvement in nodes list
- latest report button in nodes list
- nedap/pypuppetdb repo as requirement ( new api was merged nedap/pypuppetdb#17 )

puppetboard/static/css/puppetboard.css

@@ -65,3 +65,8 @@ h1.noop {
   width:20px;
   text-align:center;
 }
+.label-nothing {
+  background-color:#ddd;
+  width:20px;
+  color:#ddd;
+}