Have tag operations dialog reflect time machine configuration

If a tag deletion is going to remove images, but those images are not going to be removed immediately, we need to message that

Fixes https://www.pivotaltracker.com/story/show/143063199

static/js/directives/ui/tag-operations-dialog.js

@@ -153,6 +153,13 @@ angular.module('quay').directive('tagOperationsDialog', function () {
         }, errorHandler);
       };
 
+      $scope.getFormattedTimespan = function(seconds) {
+        if (!seconds) {
+          return null;
+        }
+        return moment.duration(seconds, "seconds").humanize();
+      };
+
       $scope.editLabels = function(info, callback) {
         var actions = [];
         var existingMutableLabels = {};