Aspace mapping changes

[ehanson8]

What does this PR do?

Several changes were made to the ArchivesSpace mapping based on the updated metadata CSV that DDC provided:

• An author field was added to the ASpace mapping and test fixtures. The standard mapping and related test fixtures were removed because they only existed for testing multiple authors which can now be tested using the ASpace mapping and test fixtures.
• A description field was added that includes the ASpace URI which also serves as the source_system_identifier. Given that the URI is now included in the description, there is no need to map it to dc.relation.isversionof.
• Rights statement and rights URI fields were added to the ASpace mapping and test fixtures.
• Several tests were updated to account for these changes

Includes new or updated dependencies?

NO