Non-urgent v1 changes

[braddf]

• 15 or 30 mins floor?
• remove delete_me locations
• refactor tests into separate files
• add integration tests for specific DP etc. functions
• refactor any duplicate functionality into reusable utilities
• Finalise rate-limiting
• model version selection?
• model versions in snapshot? Should this be everywhere or nowhere
• forecast init timestamps check all last/correct
• generation validate observers e.g. for wrong country
• /region validate region_type
• validation on forecast creation_limit_utc to be before now