[IMP] account_chart_update: Whole refactoring

* Fix calculated field when showing inactives + add field to view
* Migrated to new API.
* Provided hooks for detecting changes and for adding update/create values.
* Purge dead error detection code (not applying).
* Use global mapping dictionaries stored on class instead of passing arguments down to top and viceversa.
* Number fields computed by a function field instead of being computed by hand.
* Use recordsets as indexes instead of ids to avoid repetitive browses.
* Re-enable local cache variables
* README + authors

account_chart_update/model/account_tax_code.py

@@ -25,3 +25,13 @@ class AccountTaxCode(models.Model):
     _inherit = 'account.tax.code'
 
     active = fields.Boolean('Active', default=True)
+
+    def _sum(self, cr, uid, ids, name, args, context, where='',
+             where_params=()):
+        try:
+            return super(AccountTaxCode, self)._sum(
+                cr, uid, ids, name, args, context, where=where,
+                where_params=where_params)
+        except:
+            cr.rollback()
+            return dict.fromkeys(ids, 0.0)