Big refactoring for allowing to define recurrency at header level for simplifying
the use of the module for most of the cases where you don't need different
recurrency at line level.
Steps to reproduce the problem:
1. Log in as Mitchell Admin.
2. Create contract CNT-A for company CMP-A, assigned to Marc Demo.
3. Create contract CNT-B for company CMP-B, assigned to Marc Demo.
4. Run cron to create recurring invoices.
Actual results:
- Odoo sends automated assignment emails to Marc Demo, which indicate the name of the company activated for `__system__` user whlie the cron was being executed.
Expected results after this patch:
- Odoo sends automated assignment emails to Marc Demo, which indicate the invoice company.
@Tecnativa TT24657
* 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.
