Bug 26689: Prepend letter codes.

Bug 26689: Prepend letter codes.

This patch prepends the credit_type_code and debit_type_code with
CREDIT_ and DEBIT_ respectively when doing a lookup on the notice letter
code.

Test plan
1) As previous patches, however instead of just naming your notice to
   match the credit_type_code or debit_type_code use
   CREDIT_credit_type_code and DEBIT_debit_type_code respectively.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 87aa05f9deb7fa09f059d53b422b89c8411e0c84)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>