Drop the distinction between advisors and principals

[gjvoosten]

ANET distinguished between Advisors and Principals, but in practice this distinction doesn't always work: people can be on either side, so they could be advising or be an interlocutor, depending on context. This distinction is now removed, which means there are now flat lists of people, positions and organizations. Also the term "principal" is now avoided, and replaced by the more generic "interlocutor".

Closes AB#728

User changes

• The most important change is that report attendees can be moved freely between the Advisors and Interlocutors sections.

Superuser changes

• The most important change is that organizations no longer have a type (which was either Advisor or Principal), and that the original position types Advisor and Principal are now replaced by a single type Regular.

Admin changes

• The most important change is that people get a new property, user, which (when true) indicates that they can access ANET (i.e. login).

System admin changes

• anet.yml or anet-dictionary.yml needs change
• db needs migration
• documentation has changed
• graphql schema has changed

Checklist

• Described the user behavior in PR body
• Referenced/updated all related issues
• commits follow a repo#issue: Title title format and these 7 rules
• commits have a clean history, otherwise PR may be squash-merged
• Added and/or updated unit tests
• Added and/or updated e2e tests
• Added and/or updated data migrations
• Updated documentation
• Resolved all build errors and warnings
• Opened debt issues for anything not resolved here