If enabled, allow users and orgs to set their time machine expiration

Fixes https://www.pivotaltracker.com/story/show/142881203

static/directives/config/config-list-field.html

@@ -10,6 +10,7 @@
   <span class="empty" ng-if="!binding || binding.length == 0">No {{ itemTitle }}s defined</span>
   <form class="form-control-container" ng-submit="addItem()">
     <input type="text" class="form-control" placeholder="{{ placeholder }}"
+           ng-pattern="getRegexp(itemPattern)"
            ng-model="newItemName" style="display: inline-block">
     <button class="btn btn-default" style="display: inline-block">Add</button>
   </form>