[ADD] stock: pivot graph for stock forecast

- Task: https://www.odoo.com/web/#id=9161&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.bpogldEeqlHXzCLL
You can now use `<odoo>` instead of `<openerp><data>` tags (since commit https://github.com/odoo/odoo/commit/7c0e598c97cc48d8e55688c99db6d11ee23d9e46 )