Organization member-management

[simensandhaug]

Changes

• Implements changes from PR(change permission groups hr_group, primary_group -> admin_group, member_group)
• Add mutation to delete membership
• Add mutation to add member by username
• Ability to change membership group from member -> administrator and vice versa

Issues

• No backend tests
• Have to refresh page after delete and assign membership to see changes. Fix by updating local cache when mutating? Not sure how to do this.
• Button alignment