Create a Jupyter Notebook programatically

[tbonza]

We want to have Okra create a Jupyter notebook programatically for reporting analytics. Use the interface okra/proto/okra_api.proto to generate a mock notebook. Let's use okra/tests/mock_db.py when generating an example notebook for this ticket. The Jupyter notebook should be written to the working directory by default.

The implementation for proto/okra_api.proto is okra/repository_metrics.py. Tests for the proto/okra_api.proto implementation are tests/test_repository_metrics.py

1. Default behavior creates Jupyter notebook in working directory

okra compute https://github.com/okrahealth/okra.git

2. Option to create Jupyter notebook in specified directory

okra compute https://github.com/okrahealth/okra.git -d /tmp/

3. Naming convention for notebook should be

owner_name_hash

where owner is okrahealth, name is okra, and hash is the most recent commit hash so 5;
which would be

okrahealth_okra_5.ipynb

Normally, the commit hash would be something like df9af65674c82fbdf40777857c15aa08275934ba but we're using okra/tests/mock_db.py to implement this feature for the time being

Reference: fperez/ProgrammaticNotebook.ipynb