[REF] account: journal items reconciliation (part 1/2)

This commits refactors the code of the reconciliation, in order to facilitate the process of complex use cases, namely multi-currencies or cash-basis-taxes related (see details below). It also prepares the code for a second refactoring where we will save on each journal items the amount_currency and currency_id field (even in case of operation made in company currency), also in the sake of simplification.

1) Multi-currencies:
- the account.partial.reconcile model now will have dedicated columns to specify the amount of the partial reconciliation in the debit_line_id currency and the credit_line_id currency. That comes in handy when dealing with journal items having different secondary currencies, but also allows some simplification.
- residual_amount_currency computation changed accordingly
- moved models account.full.reconcile and account.partial.reconcile in their dedicated .py file

2) Cash basis taxes
- cash basis entries now handle correctly rounding errors to make sure the exact amount of gets reported when the reconciliation becomes full.
- the account for the base amount of cash basis entries has to be set, now, on the company instead of on each cash basis tax.
- that new 'property' field can be set at the CoA installation via the field property_cash_basis_base_account_id of account.chart.template, or going through the accounting settings.

Was task task: 2243420
Was PR #50308

Related: odoo/upgrade#1121
Related: odoo/enterprise#10252
Signed-off-by: Quentin De Paoli (qdp) <qdp@openerp.com>