Add calendar widget by copying and renaming datepicker widget files.
Remove datepicker functionality, options and methods from Calendar.
Remove calendar functionality, options and methods from Datepicker.
Adjust tests due to split and changed specification. Remove duplicated
demo files and fix some demos. Simplify calendar generation, use CSS
instead of inline styles. Fix destroy method. Make use of uniqueId
method. Fix focus highlighting when month is changed. Add version
property. Add common unit tests. Fix input keyboard handling.
