Fix #108 - Add data migration to import the Crowdtilt keys from .env

Fixes #108 - Looks like the above view exception is resolved with a database migration, but the underlying editing of bank information is still broken. 

I added a data migration to import the Crowdtilt production keys from the .env file if there's already a settings object with the necessary attributes (indicating that the site has already been initialized for payments with Crowdtilt)