PURPOSE
=======

1. Unified product demo data
2. Less demo: one per use case
3. Demo data for all models

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

1. Refactor all the brol in the demo data
2. Adapt the tests to make them green, as some products are
   renamed, removed, created in python instead of as demo data
   ...

The purpose of this commit is to handle code execution only in server
action and delegate schedule management to ir_cron model.

ir.cron model now inherits from ir.actions.server. Fields model, function
and args are removed as well as the logic to handle them. There is no
more code manipulation and evaluation in ir_cron, only a call to the run
method of ir.actions.server.

Cron form view use server action form view as primary view. This way
automated actions use the same base form as server actions with
cron details added.

Thanks to @fpodoo for the original idea and preliminary work. Thanks to
@jpr-odoo for first developments. Thanks to @jem-odoo for reviewing.

- Split compute function in res.partner into 4 functions as they no more share the same dependencies
- removed dead constraint from 'membership.membership_line' model. That constraint checks if the invoice's date
  is greater than membership line's date but the membership line is created before the draft invoice is created
  (and that too without date set), hence it can't be raised.(Though, it can be raised if we check it on 'state' field).