Create a product and price model (bug 944487)

- Create inapp app
- Create InAppProduct model
- Add a migration
Merge pull request #1789 from JaredKerim-Mozilla/944487

Create a product and price model (bug 944487)
Oops. Invert logic.
Renamed InApp migration from 751 to 754
Merge pull request #1792 from JaredKerim-Mozilla/975025

Renamed InApp migration from 751 to 754
use latest version when creating comm note for resubmission (bug 915710)
create comm notes for each review from reviewer tools (bug 947680)