Delete files to 'trash' dir

[vidartf]

The default contents manager in jupyter server will (as far as it can) send deleted files to the OS 'trash', using the send2trash package. Jupyter FS doesn't offer this option, instead files are always deleted in the manner chosen by the pyfilesystem implementation (typically without recovery options).

Since pyfilesystem doesn't have a concept of this, we are not able to it out of the box. One option could be to offer a set of implementations replacing e.g. osfs with a version that can be configured via a trait mirroring the delete_to_trash key of the FileContentsManager.