Add 'filter' glyphicon to filter panel header

netbox/templates/inc/filter_panel.html

@@ -2,6 +2,7 @@
 
 <div class="panel panel-default">
     <div class="panel-heading">
+        <span class="glyphicon glyphicon-filter" aria-hidden="true"></span> 
         <strong>Filter</strong>
     </div>
     <div class="panel-body">