Added unique constraint on email
ECOM-7085

(cherry picked from commit d141eb15)

No-op a migration that needs to be more clever

(cherry picked from commit 1e6a74e7)

model_name can be non-None, and model is still None

(cherry picked from commit 52ca02fd)

An idempotent migration to add an email uniqueness constraint

(cherry picked from commit 169414b7)

Make this no-op migration be a true no-op.

(cherry picked from commit 04557bbf)

A new django app for unicorn migrations

(cherry picked from commit 98b250b6)