[IMP] resource: Order leaves by date

Purpose
=======

Currently, `resource.calendar.leaves` are ordered
by creation date. In a list view,this is counter intuitive
if leaves are not created in the order in which
they will happen.

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

Order `resource.calendar.leaves` by `date_from`
instead of creation date.

addons/resource/models/resource.py

@@ -512,6 +512,7 @@ class ResourceResource(models.Model):
 class ResourceCalendarLeaves(models.Model):
     _name = "resource.calendar.leaves"
     _description = "Resource Time Off Detail"
+    _order = "date_from"
 
     name = fields.Char('Reason')
     company_id = fields.Many2one(