Make sure we update the calendar on date change

This introduces new property on MonthView - "today". This property is
updated by dataengine (or can be a timer too, but we already get signals
from dataengine every 30 seconds to update the clock) and is never
updated by the code itself.

Furthermore, the DayDelegate is now bound to it, so when "today"
changes, the selection rectangle in the calendar should also change.

And finally, the selected item in the grid is cleared if MonthView's
date property is cleared (which is second part of this patch, to the
applet itself).

REVIEW: 118277

src/declarativeimports/calendar/qml/DayDelegate.qml

@@ -27,7 +27,7 @@ Item {
     height: root.cellHeight
 
     property real borderOpacity: daysCalendar.borderOpacity
-    property bool today: isToday(new Date(yearNumber, monthNumber - 1, dayNumber))
+    property bool today: root.today.toDateString() == new Date(yearNumber, monthNumber - 1, dayNumber).toDateString() // for some reason the comparison doesn't work without toDateString()
 
     onHeightChanged: {
         // this is needed here as the text is first rendered, counting with the default root.cellHeight

src/declarativeimports/calendar/qml/DaysCalendar.qml

@@ -92,6 +92,14 @@ Item {
         property bool containsEventItems: false // FIXME
         property bool containsTodoItems: false // FIXME
 
+        property QtObject selectedDate: root.date
+        onSelectedDateChanged: {
+            // clear the selection if the root.date is null
+            if (calendarDays.selectedDate == null) {
+                calendarDays.selectedItem = null;
+            }
+        }
+
         Repeater {
             id: days
             model: monthCalendar.days

src/declarativeimports/calendar/qml/MonthView.qml

@@ -52,6 +52,7 @@ Item {
     property Item selectedItem
     property int week;
     property int firstDay: new Date(showDate.getFullYear(), showDate.getMonth(), 1).getDay()
+    property date today
 
     anchors.margins: borderWidth
 
@@ -98,7 +99,7 @@ Item {
         days: 7
         weeks: 6
         firstDayOfWeek: Qt.locale().firstDayOfWeek
-        startDate: today();
+        startDate: today;
     }
 
     DaysCalendar {