[IMP] account: automatically adapt account group items

Task 2092104
Accounts group Hierarchy should be automatically well done without to
have to specify the parent (based on the account group CODE)

Before, we had to set all the accounts in the correct groups manually
and it was cumbersome.
Now:
* No need to fulfill account group parent
* No need to fulfill account group id on account

We can still change the groups if there are exceptions; the groups are
only set at create and write time.