merge year and month in expected JSON

The string are already translated and in some language the order of a month in
year is year first so that needs to be handle on the translation side, which
is during the JSON generation for now.

static/src/js/calendar.js

@@ -33,8 +33,7 @@
                 var calendar_weeks_str = this.value,
                     calendar_info = JSON.parse(calendar_weeks_str);
 
-                this.calendar_year = calendar_info.year;
-                this.calendar_month = calendar_info.month;
+                this.calendar_year_month = calendar_info.year_month;
                 this.calendar_days_name = calendar_info.days_name;
                 this.calendar_days = calendar_info.days;
                 this.calendar_open = calendar_info.open;

static/src/xml/calendar.xml

@@ -14,11 +14,8 @@
                             </span>
                         </b>
                         <t
-                            t-if="widget.calendar_month"
-                            t-esc="widget.calendar_month"
-                        />&#160;<t
-                            t-if="widget.calendar_year"
-                            t-esc="widget.calendar_year"
+                            t-if="widget.calendar_year_month"
+                            t-esc="widget.calendar_year_month"
                         />
                     </div>
                     <div id="cal_body">