Account Move Line Tax Editable

This module makes the tax column on journal entry lines editable in Odoo's accounting screens, but only while the document is still a draft.

• On the invoice/bill form, in the lines list, the tax field becomes visible and editable as long as the document has not been posted. Once the document is posted, the field is locked again.
• When a user picks a different tax on a line, the module automatically finds the matching tax repartition line (the rule that decides which account and percentage the tax posts to), taking into account whether the document is a customer invoice, a vendor bill, a credit note or a refund, and whether the repartition line has an account.
• The change is applied to the account.move.line record, so the tax detail line is kept consistent with the tax chosen on the base line.

It touches the account.move.line model by adding a computed flag that says whether tax data may be edited, and by giving the tax field a write behaviour. The invoice form view account.view_move_form is extended to show and unlock the tax column. No new menus, reports, emails or scheduled actions are added.