Task 4.3 - Tracking changes and switching between versions

[mnrozhkov]

Branch: step-6-data-and-model-version-control (continue from https://github.com/iterative/course-ds-base/issues/11)

Tasks:

• [ ] add remote storage
• [ ] store file.txt to remote storage
• [ ] delete file.txt in workspace
• [ ] restore file.txt from DVC cache with dvc checkout file.txt
• [ ] clean cache with dvc gc
• [ ] try to restore file.txt from DVC cache with dvc checkout file.txt (failure is expected)
• [ ] restore file.txt from DVC Remote Storage dvc pull (success is expected)
• [ ] update 'file.txt' (version 2) and push it to remote storage
• [ ] switch btw Git branches and 'file.txt' versions