DatePicker docs (#2732)
* Add isWeekend and isWeekday functions
* Initial DatePicker docs
* Updates
* Add DateField and DateRangePicker docs
* Add section on international calendars
* Calendar docs
* RangeCalendar docs
* TimeField docs
* Updates
* More updates
* Improve calendar description
Co-authored-by: Danni <drobinson@livefyre.com>
