[EPIC] Schedule programme data model without ORM/DB

The recent programme data is continuously fetched from the Steering API. To avoid any disruption in play-out (e.g. in cases where the API is not available due to network outages) the programme is also cached locally.

Engine uses a SQLAlchemy model rebuilding an internal representation of the programme and relevant schedules for play-out.

Having an ORM and relatively heavy PostgreSQL server just for this single purpose is some unnecessary overhead. Therefore lean ways of caching should be evaluated. This POC aims to:

1. Cache the raw JSON endpoint data
2. Rebuild the ORM using simple POPOs
3. Use hashing strategies to easily detect updates, where applicable

Sub Tasks

• Extend API data fetchers to transparently cache... (#124 - closed)
• Deserialize API response using Steering/Tank Op... (#129 - closed)
• Scheduling domain objects based on POPOs (#133 - closed)
• Refactor API Fetcher
• POC for TimetableService as a lightweight replacement for ProgrammeService
• Diffing between current and planned schedule using JSON file cache
• Refactor timetable renderer for work with new domain model
• Test and integrate timetable and scheduler with new domain model
• Refactor scheduling module to improve testability
• Check if uses of ProgrammeService.engine.engine_time() can be relocated, to reduce dependencies
• Remove all references of SQLAlchemy and PostgreSQL
• Add some more test cases
• Documentation: Update README.md
• Update docs.aura.radio + Docker Compose settings

Merge Requests

• ORM-less scheduling (!35 - merged)
• ORM-less engine (aura!40 - merged)