add REST documentation for tenants module

I don't think this is right. Was it intended to be keyed by `{tenantAlias}` with `@Property   {Tenant}` ?

It would be good if we can somehow provide a paragraph description after the `@RESTModel` directive and be able to show an example, because these dynamically-keyed models are tough to understand by reading what's here. Even if Swagger doesn't provide a way to see the description on the UI (or the JSON feed), just for our own reference would be helpful. Can you give it a try and see if it trips up the parser?