Feature: Remove "plaid" references from DB models

[alexghirelli]

Type of feature

🧑‍💻 Refactor

Current behavior

We need to remove every references to "Plaid" form our DB model and make them totally agnostic in order to set the stage for our "data aggregator" package. This refactor will be vital because it allows us to store and many types of data from different data sources in one single way.

Suggested solution

• Remove all columns closely related to Plaid.
• Check the differences between Plaid and GoCardless API response payloads and try to keep the most common fields between both.

Additional context

https://developer.gocardless.com/bank-account-data/overview, https://plaid.com/docs/api/

[alexghirelli]

I'm working on this. @meglerhagen, please assign me this issue. 😄