Purpose
=======
Many values in payroll formulas change every year.
Currently, many of these values are hard coded.
A change requires the code to be updated, released, then deployed
on every server instance for changes to take effect.
This leads to formulas that are often out of date.

Specification
=============
Introduce a versioning mechanism for values
used in payroll formulas.
The mechanism should allow to encode a new value in
advance. The new value should be automatically used
when it enters into force.

Two new models are introduced:
------------------------------

Each parameter is identified by a unique code. The code is used to
retrieve its value (optionaly at a particuar date).

A parameter can have several values (aka versions).
Each version is defined by an implementation date.
The value is not valid before this date and remains valid
until the next value with a more recent date.
The system allows to request a parameter value at a particular
date.

How to use?
-----------
To retrieve a parameter value at a particular date,
use `self.env['hr.rule.parameter']._get_parameter_from_code(code, date)`.
The date is optional and set to today by default.

In a salary rule, you can directly use `payslip.rule_parameter(code)`.
The version valid at the payslip end date is automatically chosen.

#### *Note for computed fields*
This mechanism should not be used in stored computed fields!
A new parameter version can be created at any time
and we can't predict when the field is recomputed. Hence there is no
garantee that the field is up to date.
Moreover, because Odoo computes stored computed fields before
loading data, the computation will crash for existing records if it's using
a parameter defined in the same module which defines the field (the parameter
does not exist yet).

For non stored computed fields, the version date is always today
because there are no such concept of field "computed at <date>"

BE Data
=======
CO2 reference:
https://finances.belgium.be/sites/default/files/downloads/121-faq-voitures-de-societe-2019-version17.pdf
Cotisation spéciale: https://www.socialsecurity.be/employer/instructions/dmfa/fr/latest/instructions/special_contributions/companycar.html

Précompte professionel 2018:
https://finances.belgium.be/sites/default/files/downloads/700-formule-cle-20180101.pdf
Précompte professionel 2019:
https://finances.belgium.be/sites/default/files/downloads/700-formule-cle-20190101.pdf

Work bonus: https://www.socialsecurity.be/employer/instructions/dmfa/fr/latest/instructions/deductions/workers_reductions/workbonus.html

Purpose
=======

From a busines point of view

Integration with accounting. A period of pay include journal entries and
payments. We need to generate both from a batch. 

The entries must be grouped
- 1 line for salaries
- 1 line for all ATN
- ...

Payroll generate a Sepa document to send to the bank

+ as this part is managed by an accountant add menu entries in the
accounting app.

From a functional point of view: 

Debit and credit accounts are defined on the rules (hr.salary.rule)
The journal should be defined on the structure to be foced


Specification
=============

- Usability: the module l10n_be_hr_payroll Should install the accounting
  (right now it install invoicing). On the structure, add a journal m2o.

- On rule: add group accouting items on salary rule

- Improve method 'action_payslip_done' to support multiple entries by move.
  Generate only one big entry with all payslip. Generate one total line total
  for reconciable if group is set.
  Now the payslips are no longer calculated individually,
  all accounting entries are grouped together when the pay slips are
  validated.
  This allows you to have a single accounting entry for all validated
  payroll records.

- Buttons on batch
    - Add 2 buttons on the batch form 
        - "Create Entry": it will generate a grouped entries according config of
          the rule
        - "Payment": it generate an xml with all line to send to the bank
          See https://www.odoo.com/documentation/user/11.0/accounting/receivables/customer_payments/payment_sepa.html
    - Payroll directly generate the xml (no payments in accounting)

- Button on payslips: Everything should be done through the payslips 
    - create draft entry
    - Create SEPA payment xml 
    - Make appear those buttons on the form only if batch is not set 

- Belgian rules for the entries: 
    - In data for Belgium: https://docs.google.com/spreadsheets/d/1HlnwoExR_O833sij01p7UizSkrMqcm6oF4GvOeIz5lg/edit#gid=0
    example of one of our OD: https://drive.google.com/file/d/0B_hhLmdks1wEdXZSQzJIeVBDOXNiNVctczJzUTBQZVBuNkgw/view?usp=sharing

- Create a Journal salaries (type miscelaneous) and apply all structure on
  this journal

- Create new accounts to manage this.

- Sepa for payroll should be an option in the setting of payroll
  (like in accounting)

- Configure the accounts on the rules when setting a CoA on a company.

    Now the payslips are no longer calculated individually,
    all accounting entries are grouped together when the pay slips are
    validated.
    
    This allows you to have a single accounting entry for all validated
    payroll records.
    
    Other notable point in this commit:
    - When installing the Belgian Localisation or when installing the
      Belgian CoA on a company, configure the accounting data (journal,
      accounts on the salary rules)
    - Don't create automatically a payslip batch when creating a payslip

TaskID: 1935200