BookStats remaining after books have been deleted

[cblanken]

Description
I'm not sure if it's intended but it seems like BookStat records remain even when a Book has been deleted.

To Reproduce

Steps to reproduce the behavior, e.g.:

1. Start Lute with default database
2. Delete books
3. Check bookstats in SQLite Browser or via sqlite
4. See bookstats for deleted books still exist

Screenshots

For example, the bookstats after having deleted all but a few of the default books.

[jzohrab]

Whoops, not intended. Not a big deal, but should be cleaned up just for tidiness.

[jzohrab]

Thanks @cblanken for the issue. This was actually a very good catch: sqlite doesn't cascade deletes unless a pragma is set. For everything else the Lute data model took care of things properly but setting the pragma is still a good thing to do, so I added that and added a few checks and cleanup things.

Fixed in develop 👍

[jzohrab]

Launched in 3.8.0.