gui: Update to Font Awesome v5 (#4889)

gui/default/modal.html

@@ -11,7 +11,7 @@
       <div class="modal-header {{status == 'default' ? '' : 'alert alert-'+status }}">
         <h4 class="modal-title">
           <div ng-if="icon" class="panel-icon">
-            <span class="fa fa-{{icon}}"></span>
+            <span class="{{icon}}"></span>
           </div>
           {{heading}}
         </h4>