v1.2.1 fixes

[skjiisa]

Fix issues with delete functions and make them properly supported (deleting each item from the Index Set).

[skjiisa]

Not relevant to SwiftUI delete functionality, but I'm also going to use this branch and pull request to add library acknowledgements.

[skjiisa]

This last commit to allow relationships to be marked as required should fix #104.

If users already have existing hidden objects (such as modules with no games or no type), those will still remain.
I could potentially add a startup script in preloadData() to remove any objects with missing requirements.
I might not though tbh because it's not going to be a major issue and I can't imagine anyone's actually gone out of their way to make their own invalid QR codes and scanned them.