This uses a new table, 'domain_onwers' to store ownership information.

 - README: add instructions for domain ownership setup in tests
 - api.schema: add ADMIN_MODIFY_DOMAIN
 - api.admin: add PATCH /api/admin/domains/<domain_id>
 - api.admin: add PUT /api/admin/domains/<domain_id>/owner
 - api.admin: give permissions field on _get_domain_info
 - api.admin: give owner information on _get_domain_info
 - api.schema: add snowflake type


Former-commit-id: 30a77f15