Implement a rotating system for Cache, Files and potentially future store

[PonteIneptique]

Current Status: On upgrading corpora, we are saving directly onto the production "database(s)", these being Redis and the file system for reading corpora.

Goal: The new set-up should allow for a rotating system where Redis Cache, Corpora Files and the upcoming RDFLib database store ( Capitains/Nautilus#57 ) are doubled and switched from one to another in the app.py configuration. This will avoid situation where operations are on-going (in between flush and parse) and allows for bugless/no service interruption transition to a new corpora.