[FIX] account: various fixes in reconciliation

- Try to set a statement line's partner in reconciliation_widget_preprocess instead of get_reconciliation_proposition
- Sum of oldest move lines as reconciliation proposition now working for all combination of amount field / sign
- Fixed a bug where a manual reconciliation would markAsReconciled when setting mv_lines_selected during init
- Fixed a visual glitch : manual reconciliation passing in mode create while disappearing
- l10n_be_coda import was passing acc_number in the values for creating bank statements, which doesn't make sense
- In the reconciliation interface, add a clearer at the end of the 'create form'
- Do not mix payable and receivable in reconciliation proposition
- Take into account the possibility that all statement lines are reconciled when showing the reconciliation widget
- In bank statement reconciliation, handle move lines that are reconciled but not linked to a statement
- In reconciliations widgets init, set this.template_prefix before calling this._super