Change the order of Cancel and OK button in the renaming function so it matches the user experience for the same dialog boxes used in the main dashboard
Add the "Duplicate" button in the main dashboard

so we can copy an existing notebook without having to start it's instance
update add_duplicate_button with API changes

- allow duplicating regular files
- update with contents service API changes
- fix some path/name bugs found in session and kernel list
set min-width on tree-list buttons

avoids misaligned buttons when the content changes
simplify NotebookList.duplicate with recent changes

- contents service + futures
- remove no-longer-necessary parent_item
Merge pull request #6916 from minrk/finish-5659

add Duplicate button to dashboard