Replace only use of crystal_project icons with FA.

This means we can remove the crystal_project icons when removing
the old templates.

modules/statistics/templates/statistics.twig

@@ -16,7 +16,7 @@
     <table class="selecttime">
         <tr>
             <td class="selecttime_icon">
-                <img src="/{{ baseurlpath }}resources/icons/crystal_project/kchart.32x32.png" alt="Report settings" />
+                <i class="fa fa-pie-chart"></i>
             </td>
             <td>
                 <form action="#">
@@ -66,7 +66,7 @@
     <table class="selecttime">
         <tr>
             <td class="selecttime_icon">
-                <img src="/{{ baseurlpath }}resources/icons/crystal_project/date.32x32.png" alt="Select date and time" />
+                <i class="fa fa-calendar"></i>
             </td>
             {% if available_times_prev %}
             <td><a href="{{ get_times_prev }}">&laquo; Previous</a></td>