[IMP] estate: Add a server action for better UX

Problem
---------
Users may want to cancel several houses and flats at once, currently
this is not possible; they have to do it one by one.

Objective
---------
Add a way to cancel several estates in one go.

Solution
---------
Add a server action in the demo data so that it is available for new
users. Old users can create the same server action on their database.

task-123456

estate/__manifest__.py

@@ -20,4 +20,7 @@
 
     ],
     'license': "LGPL-3",
+    'demo': [
+        "demo/demo.xml",
+    ],
 }

estate/demo/demo.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<odoo>
+    <data>
+        <record id="model_estate_property_action_cancel" model="ir.actions.server">
+            <field name="name">Mass cancel</field>
+            <field name="model_id" ref="estate.model_estate_property"/>
+            <field name="binding_model_id" ref="estate.model_estate_property"/>
+            <field name="binding_view_types">list</field>
+            <field name="state">code</field>
+            <field name="code">action = records.action_cancel()</field>
+        </record>
+    </data>
+</odoo>

estate/models/estate_property.py

@@ -46,3 +46,8 @@ class Property(models.Model):
     tag_ids = fields.Many2many("estate.property.tag", string="Tags")
 
     offer_ids = fields.One2many("estate.property.offer", "property_id", string="Offers")
+
+    def action_cancel(self):
+        state = self.state
+        if state != 'cancelled':
+            self.state = 'cancelled'