Workflow revision for deleting an instrument name in a multi-source setting

[PouyaMohseni]

Previously, we only considered one source and one contributor per instrument name, allowing defining deletion of an instrument by the contributor (#274). With the definition in #436, instrument names can now be contributions from several people, each providing a different source or endorsing the same sources. Therefore, the deletion workflow should be reconsidered.

It is clear that a person should be able to remove their own contribution (here, the name-source relation they provided). Accordingly, an instrument name is deleted only when all contributors remove their contributions.

However, what about other aspects and the interplay of superuser?

[PouyaMohseni]

Also, delete contribution to an instrument name might be useful, where it removes all sources contributed by the user to that instrument name.