[IMP] account, base_import: improve accounting import

- Remove FEC from res.config.settings - everything is now linked in the import guide (in enterprise)
- Compute debit and credit from opening_balance
- Update import templates for account.account, account.move, res.partner
- Small UI changes in base_import: add an action title and improve the template button design

task-2888243

closes odoo/odoo#96291

Related: odoo/enterprise#29627
Related: odoo/upgrade#3794
Signed-off-by: Cedric Snauwaert <csn@odoo.com>

odoo/addons/base/models/res_partner.py

@@ -1006,7 +1006,7 @@ class Partner(models.Model):
     def get_import_templates(self):
         return [{
             'label': _('Import Template for Customers'),
-            'template': '/base/static/xls/res_partner.xls'
+            'template': '/base/static/xls/res_partner.xlsx'
         }]
 
     @api.model