Fix placement of calendar window

Before, the placement wasn't correct for smaller or bigger font sizes.

For some reason, window->Bounds() always returns the coordinates of the
CalenderMenuWindow's ctor, BRect(0.0, 0.0, 100.0, 130.0), not the actual
size.
Using GetLayout()->PreferredSize() instead works...

src/CalendarButton.cpp

@@ -130,7 +130,12 @@ CalendarButton::ShowPopUpCalendar()
 
 	BDate date = fDateBox->GetDate();
 	BMessage* invocationMessage = new BMessage(M_SET_DATE);
-	BPoint where = Bounds().LeftTop();
+
+	// Get the center of the BButton
+	BRect buttonRect(Bounds());
+	BPoint where = buttonRect.LeftTop();
+	where.x += buttonRect.Width() / 2;
+	where.y += buttonRect.Height() / 2;
 	ConvertToScreen(&where);
 
 	CalendarMenuWindow* window = new CalendarMenuWindow(this, where);
@@ -139,7 +144,5 @@ CalendarButton::ShowPopUpCalendar()
 	window->SetDate(date);
 	fCalendarWindow = BMessenger(window);
 	window->Show();
-
-	window->MoveBy(Bounds().Width() / 2, window->Bounds().Height() * -1.5);
 	window->MoveOnScreen(B_MOVE_IF_PARTIALLY_OFFSCREEN);
 }

src/CalendarMenuWindow.cpp

@@ -118,6 +118,9 @@ CalendarMenuWindow::CalendarMenuWindow(BHandler* handler, BPoint where)
 	groupView->AddChild(view);
 	AddChild(groupView);
 
+	// Moves the bottom left corner of the window to "where"
+	BSize size = GetLayout()->PreferredSize();
+	where.y -= size.height;
 	MoveTo(where);
 }