[FIX+IMP+MIG] contract: Several refinements:

* Remove incorrect oldname attributes.
* Add filter on partners for running contracts (+ a support o2m field for that).
* Cover more tables in model renaming + cleaner code using a loop.
* Don't copy contract lines, but rename table + copy contract records on pre.
* Contract code is now populated to "Reference/Description" field in invoice.
* Order on new contract model has been restored to the same as old analytic accounts.

contract/models/contract_line.py

@@ -25,7 +25,6 @@ class ContractLine(models.Model):
         required=True,
         index=True,
         ondelete='cascade',
-        oldname='analytic_account_id',
     )
     analytic_account_id = fields.Many2one(
         string="Analytic account",