Change cmp to att in Source relationships

[ahankinson]

The cmp relator code in the 700 has the label "Composer cross-reference" and is used to create a link between a person and their possible role in composing a piece. However, the cmp relator code has a meaning of a definite composer attribution, while the intent of the composer cross-reference is to add a person who was simply attributed to the creation of the piece. (whether or not they actually did.)

For this purpose, the att relator code in Sources is a better fit for the intended purpose of this code.

This will help clarify the intent of the relationship since the data that is exported from Muscat does not contain the "cross reference" qualifier, and simply states cmp, which (in most cases) is wrong.

As agreed, for Sources, the cmp relator code should be changed to att. The label in the drop-down can stay the same (unless somebody else feels otherwise).

All existing instances of cmp in Sources can be changed to att for the 700 field relationship.

See the Muscat meeting notes of 4 and 11 December 2024 for background.

[ahankinson]

@BernLutz