Fix[BB-458]: Showing error conflict page on deleting entity twice

[tr1ten]

Problem

fixing BB-458 bug

Solution

show error conflict page when user tries to delete same entity twice.

Areas of Impact

1. src/server/routes/entity/author.js
2. src/server/routes/entity/edition-group.js
3. src/server/routes/entity/edition.js
4. src/server/routes/entity/publisher.js
5. src/server/routes/entity/series.js
6. src/server/routes/entity/work.js

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[MonkeyDo]

That's great, now it's a bit safer and we can't double-delete entities.

Thanks for your efforts !
In comparison to the other PRs, this one was a bit more involved and I think you did absolutely great finding your way through this complicated codebase !
Well done 🎉