Add Calendar and supporting components.

Adds: Calendar, CalendarModel, CalendarHeaderModel, CalendarStyle,
RangedDate, DateUtils and relevant tests.

Task-number: QTBUG-29948

Change-Id: Ibdd3923c514908cf8707f8572748e43a6eadbdfc
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>