- Admin users can always do everything

- Assist users can do according to their meta values set to "true":
  - allow.admin.user
  - allow.admin.booking
  - allow.admin.event
  - allow.admin.config
  - allow.admin.see-menu

  - allow.calendar.see-past
  - allow.calendar.see-data
  - allow.calendar.create-single-bookings           (requires calendar.see-data)
  - allow.calendar.cancel-single-bookings           (requires calendar.see-data)
  - allow.calendar.delete-single-bookings           (requires calendar.see-data)
  - allow.calendar.create-subscription-bookings     (requires calendar.see-data)
  - allow.calendar.cancel-subscription-bookings     (requires calendar.see-data)
  - allow.calendar.delete-subscription-bookings     (requires calendar.see-data)
