Fix month and year not getting updated after reseting date to today

The old code forgot to launch some signal by directly assigning todat to
the displayed date. Using the setter make sure everything is displayed
visually.

src/declarativeimports/calendar/calendar.cpp

@@ -84,9 +84,8 @@ void Calendar::setToday(const QDateTime &dateTime)
 
 void Calendar::resetToToday()
 {
-    m_displayedDate = m_today;
+    setDisplayedDate(m_today);
     updateData();
-    Q_EMIT displayedDateChanged();
 }
 
 int Calendar::types() const