Add Calendar to Qt Quick Controls.

Task-number: QTBUG-29948

[ChangeLog][QtQuickControls] Calendar was added. Calendar allows
selection of dates from a grid of days, similar to
QCalendarWidget.

Change-Id: I279130e704bc0dfd8dfe114ec9b6b49e111faf96
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>