Perform these two SQL calls & check their result:
- `PRAGMA integrity_check`
- `PRAGMA foreign_key_check`:
See https: //www.sqlite.org/pragma.html for more info on these.
This also removes the unused `PeriodicMaintenanceLoop()` function.
Periodic checking while Flamenco Manager is running might be introduced
in a future commit, after the startup-time checks have been shown to not
get in the way.
