Create Python frozen requirements file

[pombredanne]

We need to create Python frozen requirements file: this may need a specific convention as a requirements file is not your typical lockfile-only format. We likely want to use using pip freeze.

[pombredanne]

For info, the lockfile is named requirements.deplock

[keshav-space]

As suggested by @pombredanne, use pip inspect instead of pip freeze. #25

pip freeze does not include the relationship between dependencies. Instead, use pip inspect to get the JSON report of the Python environment, which includes the dependency relationships, and store it in the pip-inspect.deplock file.