Organizations own Users

Add ability for Organizations to own Users. There's already enterprise users and the defunct GMA that associate top level groups with users.

The users in this issue are directly associated as owned by the organization in a similar sense to Enterprise Users.

This could be as simple as having an organization_id column on the users table. There is currently an organization text DEFAULT ''::text NOT NULL field on the user_details table.

Enterprise Users have the provisioned_by_group_id column on the user_details table.

GMA has the managing_group_id column on the users table.

Probably default organization_id = 1.

Note that there is another kind of organization - user relationship with Users with access to an Organization (#415418 - closed)