Fixes #141

- add `includeVirtual` as GET parameter for `json_playout()`
- refactor `json_playout` to be cleaner

Closes: #120

- remove remaining usage of naive datetime objects
- refactor json_day_schedule and json_playout views
- remove unused methods in TimeslotManager

- Run as aura with AURA_UID
- Use WORKDIR /app
- Install Poetry in /opt/poetry

- Add choices for freq
- Add choices for by_set_pos
- Add unique_together