Fix navigation tree to take into account ordered folder

Steps to reproduce:

1. Create an Ordered folder
2. Create 3 folders in this ordered folder with the following title
   • first document title= AAA
   • second document title = ZZZ
   • third document title = CCC
3. Navigate back to the ordered folder and observe that:

• the content view displayed the documents in the expected order (AAA then ZZZ then CCC)
• the navigation tree displays the documents sorted by title: AAA then CCC then ZZZ

This is probably due to the fact that the nuxeo-document-tree element uses the tree_children page provider which sorts by title.

In the JSF UI, there was a custom logic in DocumentTreeNodeImpl#fetchChildren to handle orderable nodes.