Establish storage for calculated product footprints

Priority: Low;
Estimated person-hours: 5
Volunteer(s)/Candidate(s): None

Functional specifications: Although product footprints may be produced on the fly from the the [Direct Requirements Matrix](https://github.com/BONSAMURAIS/bonsai/wiki/Glossary#direct-requirements-table), the calculated footprints may need to be stored (temporarily) to allow more speedy access.
Technical specifications: Provide a store for calculated [product footprints](https://github.com/BONSAMURAIS/bonsai/wiki/Glossary#product-footprint) in a form that makes them quickly accessible for web-queries, e.g. as csv files.

_Relates to #10, copied from [here](https://github.com/BONSAMURAIS/bonsai/wiki/Data-Storage#clarification-of-minimum-security-issues) with minimal editing for quality._

Start by reading the Direct Requirements Matrix and the linked definitions of product footprints, then inspect how footprints are currently calculated and exposed to web queries. Determine a suitable temporary storage format, such as CSV, and document the access path and retention expectations. Done means calculated product footprints are stored and quickly retrievable for web queries.

Written by the indexing model from the issue text.