Add username for guests

https://jira.usit.uio.no/browse/CRISTIN-127

Det kan være greit å se gjennom denne commit for commit.

• Add username from IGA for guests
• Don't cache IGA data
• Refactor cristin_xml.add_persons()
• Make cristin_xml.add_persons() keyword only
• Refactor get_guest_employees function
• Upgrade abstract-iga-client to v3.1.0
• Refactor get_iga_data function
• Add type annotation