show Date Created for things in react files

closes: #CNVS-12640
closes: #CNVS-12713

test plan:
* make sure "Date Created" column shows up between
  "Name" and "Date Modified" when viewing a folder
  or search results

Change-Id: I8261eb30a5bb6e05e9cf9a3b2cccd4eba633d48c
Reviewed-on: https://gerrit.instructure.com/38921
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>

app/coffeescripts/react_files/components/ColumnHeaders.coffee

@@ -11,6 +11,10 @@ define [
     displayName: 'Name'
     property: 'name'
     className: 'ef-name-col'
+  ,
+    displayName: 'Date Created'
+    property: 'created_at'
+    className: 'ef-date-created-col'
   ,
     displayName: 'Date Modified'
     property: 'updated_at'

app/coffeescripts/react_files/components/FolderChild.coffee

@@ -27,6 +27,8 @@ define [
             Link to: 'folder', contextType: @props.params.contextType, contextId: @props.params.contextId, splat: @props.model.urlPath(),
               i className:'icon-folder',
               @props.model.get('name')
+        div className:'ef-date-created-col',
+          FriendlyDatetime datetime: @props.model.get('created_at'),
         div className:'ef-date-modified-col',
           FriendlyDatetime datetime: @props.model.get('updated_at'),
         div className:'ef-modified-by-col',

app/stylesheets/pages/ember_files.scss

@@ -245,6 +245,13 @@ $border: #e5e4e4;
       -ms-flex: 8 0;
     }
 
+    .ef-date-created-col{
+      flex: 3 3 0;
+      -webkit-flex: 3 3 0;
+      -ms-flex: 3 0;
+      @include hideForPhone;
+    }
+
     .ef-date-modified-col{
       flex: 3 3 0;
       -webkit-flex: 3 3 0;