Restore aborted session

[tasooshi]

It should be possible to restore a session, a switch accessible both from CLI and from the API.

[tasooshi]

Since this is much of an overhead, it should be user's decision to enable this kind of machinery

[tasooshi]

One idea is to dump tasks list to a CSV/JSON in case of KeyboardInterrupt or on exception while in the loop, and adding an option to load from a file.