[ADD] account_payment_base_oca: New base module for OCA/bank-payment

[alexis-via]

Work in progress. Expect datamodel changes.

[pedrobaeza]

Why this? Why didn't you answer to my comment in the issue? I don't want data model changes if they are not justified.

[alexis-via]

I'm trying to adopt the new datamodel. I'm not saying it's the best choice, but I want to try and see what difficulties I face.
I now have the full stack working: account_payment_base_oca + account_payment_order + account_banking_pain_base + account_banking_sepa_credit_transfer + account_banking_mandate + account_banking_sepa_direct_debit. So I am able to make full scenarios and see the real problems I face and try to address them.
At the moment, it's too early to list them, because I'm currently performing the tests.