fix: Stable build in app/base/models.py

[Tumble17]

Migrated models.py to flask-sqlalchemy data structures

This PR uncovered an error with the app/base/models.py when trying to run the build instructions.

The script was trying to make use of sqlalchemy structure: Binary, Column, Integer, String. Few different ways to tackle this issue, such as importing sqlalchemy itself, but making use of the available imports was chosen to reduce changed touchpoints. Data structures are available through the db, which is created in the init script.

Tested locally and results in a stable run. Hopefully you agree and we can update this file to allow this repo to be used easily.

Please let me know if you want to change anything to align to your ways of working and standards, I cannot see a contribution file.