Tenants view

[alexweininger]

A new view for viewing and managing tenants. It would be collapsed by default and below the Resources and Workspace views.

1. Be able to see all tenants for the signed in account, and possible multiple accounts if we can support that
2. Select and deselect tenants. Only subscriptions from selected tenants should show up in the Resources view.
3. See when a tenant requires additional authentication and allow the user to start the auth process for those tenants

I also want to think about how this would work if other Azure (non v2 api) extensions want to leverage a similar view.