Feature/sckan 274

[afonsobspinto]

closes https://metacell.atlassian.net/browse/SCKAN-274

• Adds synonym model
• Adds migration that creates synonym model
• Adds migration that moves duplicated anatomical entities to the synonyms. Keeps as primary anatomical entity name, the first name found.
• Adds migration to make ontology uri unique for anatomical entities
• Adds migration to remove unique name constraint for anatomical entities (after discussion with @ddelpiano)
• Updates django ingest anatomical entities command to work with the new file and with the new model. Adds update_names flag to allow overwrite of the primary anatomical entities label.

See https://metacell.atlassian.net/browse/SCKAN-274?focusedCommentId=14056 for some tests