Use fileId instead of path in the store

[hbcarlos]

fixes #165

Use fileId instead of path in the store.

If we use the path instead of the file ID, when renaming the file and creating a new file with the old name, the new file will have the updates of the old one (Kind of. If the content on disk differs from the store, the disk has priority).

[github-actions]

👈 Launch a Binder on branch hbcarlos/jupyter-collaboration/fix#165_

[SylvainCorlay]

As per discussion with Carlos, if this gets in, it may require a change in jupyverse. Ping @davidbrochart for awareness.

[davidbrochart]

Jupyverse already implements this here. I suggest to get rid of path.parent:

updates_file_path = f".{file_type}:{file_id}.y"

[davidbrochart]

Thanks @hbcarlos