* restore: improved user experience
* 'snapshot restore' is now the same as 'restore' and both will
support restoring by manifest ID, root ID or root ID + subdirectory
* added support for restoring individual files
* implemented PR feedback and refactored object ID parsing
Moving helpers inside the snapshot/ package helped clean up the code
a lot.
* This is 99% mechanical:
Extracted repo.Repository interface that only exposes high-level object and manifest management methods, but not blob nor content management.
Renamed old *repo.Repository to *repo.DirectRepository
Reviewed codebase to only depend on repo.Repository as much as possible, but added way for low-level CLI commands to use DirectRepository.
* PR fixes
