CC-3722: Create loading indicator for AJAX call when calculating Show length

- done

airtime_mvc/application/views/scripts/form/add-show-when.phtml

@@ -46,6 +46,7 @@
         </dt>
         <dd id="add_show_duration-element">
             <?php echo $this->element->getElement('add_show_duration') ?>
+            <img id="icon-loader-small" src="/css/images/loader-small.gif" style="vertical-align:middle; display:none;"/>
         </dd>
         <?php if($this->element->getElement('add_show_duration')->hasErrors()){ ?>
                 <ul class='errors'>

airtime_mvc/public/js/airtime/schedule/add-show.js

@@ -460,9 +460,12 @@ function setAddShowEvents() {
     })
 
 	function calculateDuration(endDateTime, startDateTime){
-		var duration;
+		var loadingIcon = $('#icon-loader-small');
+		
+		loadingIcon.show();
 		$.post("/Schedule/calculate-duration", {startTime: startDateTime, endTime: endDateTime}, function(data){
 		    $('#add_show_duration').val(JSON.parse(data));
+		    loadingIcon.hide();
 		});
 	}
 }