The commit 0679d0d introduced a new
planning mechanism for the workorder. Two issues have been instroduced
since this patch.
1. Cancelling a workorder didn't free the time slot in the workcenter
calendar
2. Validation a workorder sooner than the planned date didn't update
the workcenter calendar to plan another production sooner.
This commit update the date_planned_start and date_planned_finished
at cancellation and validation to impact the workcenters calendar.
To keep the original planning dates, they are now tracked
This commit also fix the button_start() method that always rewrited the
date_start even if the production had already been started.
Task : 2082442
closesodoo/odoo#38947
X-original-commit: 4ca6c773a00320865142e4efb3645f36c54ce9a2
Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>