Makes screenreaders read folder names

In order to take advantage of this, all the nodes of the tree must
have an aria-label.

closes CNVS-17947

Test Plan:
   - Go to New Files
   - Using VO go to the folder tree structure
   - When you follow the directions as read (up/down, etc.) you
     should be read the names of the folders.
   - The same should also be true where this same tree is used
      (outcomes)

Change-Id: I04b502fb0d86fc17aa3f9c6b4b7c20d8d03f2885
Reviewed-on: https://gerrit.instructure.com/47483
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Tested-by: Jenkins
QA-Review: Nathan Rogowski <nathan@instructure.com>
Product-Review: Clay Diffrient <cdiffrient@instructure.com>

Author: claydiffrient

app/coffeescripts/react_files/components/MoveDialog.coffee

@@ -66,7 +66,11 @@ define [
     render: withReactDOM ->
       form { ref: 'form', className: 'form-dialog', onSubmit: preventDefault(@submit)},
         div {className: 'form-dialog-content'},
-          div ref: 'FolderTreeHolder'
+          aside {
+            role: 'region'
+            'aria-label' : I18n.t('folder_browsing_tree', 'Folder Browsing Tree')
+          },
+            div ref: 'FolderTreeHolder'
         div {className: 'form-controls'},
           button {
             type: 'button'

app/coffeescripts/views/TreeBrowserView.coffee

@@ -78,6 +78,7 @@ define [
       @$tree.find('[role=treeitem]').not($to).attr('aria-selected', false).removeClass(@focusStyleClass)
       $to.attr 'aria-selected', true
       $to.addClass(@focusStyleClass)
+      $.screenReaderFlashMessageExclusive($to.attr('aria-label'))
       toId = $to.attr 'id'
       if not toId
         toId = _.uniqueId 'treenode-'