Prevent orphaned contact cards

[charludo]

DRAFT until #3169 is merged

Short description

Prevent the deletion of contacts as long as pages/pois/events still referr to it. Note that no list of objects referring to the contact in question is shown in the error message, since we show that list in the contact details anyways.

Proposed changes

• prevent deletion of contacts in the edit view
• prevent deletion in the bulk action view

Side effects

• none

Resolved issues

Fixes: #3260

---

Pull Request Review Guidelines

[MizukiTemma]

@charludo
Could you add the same check for archiving too? 😸

[charludo]

@charludo Could you add the same check for archiving too? 😸

done

[MizukiTemma]

Thank you for the PR, the protection functions as expected 😸

I have some suggestion for improvement:

1. Can we probably add to the tests such cases that archiving/deleting is prevented due to referring contents?
2. It's even more cool if error messages are bundled that appear when contacts cannt be bulk archived/deleted, like the corresponding success messages?
3. Deactivating the buttons if the contact is protected: you can open an issue for this if you think better to separate.

[charludo]

1. Can we probably add to the tests such cases that archiving/deleting is prevented due to referring contents?

Absolutely!
But more importantly: I had not realized how much preparation you had already made for this - thank you so much! It was a breeze to add the tests thanks to you!! 💛

2. It's even more cool if error messages are bundled that appear when contacts cannt be bulk archived/deleted, like the corresponding success messages?

Done!

3. Deactivating the buttons if the contact is protected: you can open an issue for this if you think better to separate.

Done!

[MizukiTemma]

Thank you 😸

[JoeyStk]

Thank you very much!
This looks really good 🚀