[Pending review] As a new org user, I want to type organization name instead of First/Last name on register & edit account forms

- [x] Add `only_organizations` to `community`
- [x] When registering, show Organization name instead of First/Last if only organizations. Store it as `given_name`
- [x] At edit user form, show org name, instead of first/last if `is_organization`
- [x] Add `is_organization` to `people`