[19.0][MIG] sale_commission_oca: Migration to 19.0

[pablo-cort-s73]

sale_commission_oca: Migration to 19.0

• Documentation updated (README.rst and static/description/index.html) by pre-commit – OCA banner added and badges/licence corrected (‘licence’ instead of ‘licence’).
– All links in branch 18.0 → 19.0 updated (GitHub, Weblate, Runboat, feedback…).
– Heading levels adjusted in generated HTML.

• The module version in manifest.py is upgraded from ‘18.0.1.0.0’ to ‘19.0.1.0.0’.

• In the Python code (models):
– ORM command tuples ((6,0,…), (0,0,…), (4,id)) are replaced by the odoo.fields.Command API (set, create, link).
– Domain() is used to return searches in _search_agents().

• In the tests:
– Command is imported and used to create/link agents and sales orders.
– References to demo data (agent_monthly, commission_section_*) are removed.

• In the sale_order_view.xml:
– The obsolete invisible fields commission_free and invoice_lines are removed.