Format TTL for humans

When viewing details of events with a long TTL, it is not
straightforward to check if it is about to expire or not.

Instead of displayer the raw TTL as a number of seconds, format it by
using an appropriate unit of time and fixed precision:
  * 42 => "42 seconds"
  * 420 => "7.0 minutes"
  * 4200 => "70.0 minutes"
  * 42000 => "11.7 hours"
  * 420000 => "4.9 days"

lib/riemann/dash/public/eventPane.js

@@ -1,5 +1,19 @@
 // Pane at the bottom of the dashboard for displaying events in context.
 
+function format_ttl(ttl) {
+  if (parseInt(ttl) != ttl) {
+    return ttl;
+  }
+
+  if (ttl > 3600 * 48) {
+    return (ttl / 3600 / 24).toFixed(1) + " days";
+  } else if (ttl > 3600 * 2) {
+    return (ttl / 3600).toFixed(1) + " hours";
+  } else if (ttl > 60 * 2) {
+    return (ttl / 60).toFixed(1) + " minutes";
+  }
+  return ttl + " seconds";
+}
 var eventPane = (function() {
   var el = $('#event-pane');
   var fixedFields = ['host', 'service', 'time', 'state', 'metric', 'ttl', 'description', 'tags'];
@@ -11,7 +25,7 @@ var eventPane = (function() {
       '<span class="state {{-state}}">{{-state}}</span>' +
       '<span class="metric">{{-metric}}</span>' +
       '<time class="absolute">{{-time}}</time>' +
-      '<span class="ttl">{{-ttl}}</span>' +
+      '<span class="ttl">{{-format_ttl(ttl)}}</span>' +
       '<span class="tags">{{-tags}}</span>' +
       '</div>' +
       '<pre class="description">{{-description}}</pre>');