[IMP] project: Calendar view by month on project.task

Purpose:
The field date_deadline is a date field (without hours:minutes:seconds)
The customer is tempted to put the task deadline under hours, which is not
feasible

So in the calendar view for task, set the "month" view by default
instead of the "week" view.

addons/project/project_view.xml

@@ -399,7 +399,7 @@
             <field name="model">project.task</field>
             <field eval="2" name="priority"/>
             <field name="arch" type="xml">
-                <calendar color="user_id" date_start="date_deadline" string="Tasks">
+                <calendar color="user_id" date_start="date_deadline" string="Tasks" mode="month">
                     <field name="name"/>
                     <field name="project_id"/>
                 </calendar>