Add a copy capability to jupyter notebooks

[agrippa]

This is a small change to add the ability to copy files in the Notebook UI, in addition to moving them. Because of my infamiliarity with the notebook code base, I tried to minimize the amount of changes necessary to achieve this. Mostly, this appropriates the same code paths as Move but adds a keep_old flag that indicates whether the source file should be cleared out (move) or not (copy).

This is my first pull request on the repo, so apologies if I skipped/mangled a whole bunch of steps in creating this pull request (as I imagine I may have).

[takluyver]

Thanks! It will probably be a few days before I can look at this properly, but someone else might be able to have a look sooner.

It looks like the CI tests have failed - can you have a look and see if that's related to the change you made?

There is already a method ContentsManager.copy() in the API - maybe it's possible to use that?

[dibyadas]

@agrippa I think version changes automatically when start developing the code base. And should be changed when we are making a PR, if I'm not mistaken.
I'm currently new to the codebase so I might be wrong in this. 😄

[takluyver]

ContentsManager already has a copy() method - can we try using that rather than adding a parameter to rename()? Or is there some reason that won't work?

[agrippa]

@takluyver Thanks for the feedback! I looked at just using copy() and did a bit of refactoring, is that along the lines of what you were thinking?

[takluyver]

That's a start, but I don't think we need the keep_old parameter anywhere - the contents manager class already has a copy() method separate from rename(). Maybe we need to expose it to the notebook UI.

[Zsailer]

Thanks, @agrippa, for this work!

This has been inactive for awhile, so I'm going to close this PR for now.

I think it's a good feature to add at some point, but it looks like developer time is limited here. If anyone has time to devote to it, feel free reopen or resubmit a new PR.

Thanks!