Add custom relationship capabilities to the contrib module

[Kircheneer]

No description provided.

[mzbroch]

@Kircheneer How can we help to get this to the final line? We'd like to see this in, so we can remove dependency. Also we can help with testing.

[Kircheneer]

@mzbroch I would appreicate testing in this case. Giving this a go in a real-world scenario would enhance my confidence it actually works.

[Renrut5]

@Kircheneer I have been using this in a real world case and it's working fully outside of one thing: if the object doesn't yet exist in the database, it'll raise a warning %s matching query does not exist.

This seems to be happening on one to one relationships of the same object type, but it doesn't seem to impede functionality as the relationships are still created in the database.

[Kircheneer]

Thanks @Renrut5 - I will try and push this forward then.

[Kircheneer]

Added docs and fixed linting. Ready for review.

[jdrew82]

LGTM!

[Renrut5]

@Kircheneer, just found a bug in it so don't merge yet. Did find a potential fix, but need to verify.

[Renrut5]

@Kircheneer , it appears the issue was already addressed in your most recent commit. I have nothing to prevent merging at this time.