Change unique key constraint on users from 'username+origin' to 'username+identity_provider_id'
 - Users can now be created with the same username if they are in different IDPs.

[#82406674] https://www.pivotaltracker.com/story/show/82406674

Signed-off-by: Rob Szumlakowski <rszumlakowski@pivotal.io>
Add users.identity_zone_id not null constraint

[#82406674] https://www.pivotaltracker.com/story/show/82406674

Signed-off-by: Rob Szumlakowski <rszumlakowski@pivotal.io>
Add subdomain to activation links in emails.

[#82406674]