- Add a `CheckpointManager` base class and infrastructure for creating a
`checkpoint_manager` instance attribute on `ContentsManager`.
- Provide default implementations of `delete` and `rename` in the base
`ContentsManager` class. `ContentsManager` subclasses are now
required to implement `delete_file` and `rename_file`. These methods
no longer need to manage checkpoints.
- Move checkpoint-related functionality from `FileContentsManager` to a
dedicated `FileCheckpointManager` subclass.
- Move shared filesystem interaction logic into `FileManagerMixin`
used by both `FileContentsManager` and `FileCheckpointManager`.
- Minor tweaks to ContentsManager tests to get methods from the right
object.
The purpose of this change is to provide an API for users to replace
just the checkpoint logic associated with a particular
`ContentsManager`. In particular, this change makes it possible to
easily support remote storage of checkpoints while otherwise retaining
normal filesystem interactions.
- start with no number (Untitled0 -> Untitled.ipynb)
- copy of copy increments instead of adding another `-Copy` (copy Foo-Copy1.ipynb gives Foo-Copy2.ipynb, not Foo-Copy1-Copy1.ipynb)
- copy file to new folder starts with the original filename, instead of unconditional `-Copy0`
- path is full path (including name)
- name is only used for read-only convenience, and plays no role in any API
- remove 'untitled upload' (POST with content and no path)
