Vault db tasks

Add new rake task for pulling the DB schema for testing from vault instead of payments and remove payments tasks.

Like the previous payments_db_tasks, vault_db_tasks is split into two parts. There' is a pull_vault_schema that copies the migrations into contrib, and a create_payments_db task that uses sequel to run those migrations out of the local contrib directory. This is split into two because cloning the migrations requires secure credentials that a CI server won't have.