Better support for attributes in sigma migrations

[KevinDCarlson]

Closes #825, allowing sigma-migrations along functors out of schemas with attrtypes, as long as acset morphisms are assumed to be tight.

[github-actions[bot]]

Review Checklist

Does this PR follow the development guidelines? Following is a partial checklist:

Tests

• [x] New features and bug fixes have unit tests
• [x] New modules have tests that are ultimately called by the test runner (test/runtests.jl)
• [x] Existing tests have not been deleted
• [x] Code coverage >= 90% or reduction justified in PR

Documentation

• [x] All exported functions, types, and constants have docstrings, written in complete sentences
• [x] Citations are given for any constructions, algorithms, or code drawn from external sources

Other

• [x] Style guidelines are followed, including indent width 2
• [x] Changes breaking backwards compatibility have been approved

[epatters]

@KevinArlin, did you forget to push a commit? I see that Kris' comments are resolved but not any changes.

[KevinDCarlson]

@KevinArlin, did you forget to push a commit? I see that Kris' comments are resolved but not any changes.

Thanks, yeah, looks like it.