Display description using a monospaced font

Some metrics can contain multiple lines of output generated by a CLI
program that aligned information for bettear readibility (e.g. ps(1)
output of the cpu metric from riemann-health).

Swicth to a PRE tag to display this content preserving spacing.

lib/riemann/dash/public/eventPane.js

@@ -14,7 +14,7 @@ var eventPane = (function() {
       '<span class="ttl">{{-ttl}}</span>' +
       '<span class="tags">{{-tags}}</span>' +
       '</div>' +
-      '<div class="description">{{-description}}</div>');
+      '<pre class="description">{{-description}}</pre>');
 
   var rowTemplate =
         _.template("<tr><td>{{-field}}</td><td>{{-value}}</td></tr>");

lib/riemann/dash/views/css.scss

@@ -174,6 +174,7 @@ html,table {
     float: left;
     clear: both;
     white-space: pre-wrap;
+    margin: 3px;
   }
 }