Calendar: Add calendar widget

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.
Calendar: Add min and max option.

Improve render day cell mechanism.
Calendar: Remove select callback reference
Datepicker: Code clean up for events
Datepicker: Remove unwanted keyboard shortcut

Remove shortcut for closing the calendar and erasing the date (CTRL+END).
Remove unwanted CTRL+HOME shortcut and support for enter key on input.
Datepicker: Simplify usage of calendar options and avoid duplications
Datepicker tests: Add open and close unit tests
Datepicker: Improve document click event
Calendar: Fix broken day table cell attributes
Datepicker tests: Rewrite event unit tests
Calendar: Fix multiple calendar styles
Calendar: Fix German localization
Datepicker: Fix localization demo
Datepicker: Several minor code improvements

Several minor code improvements and make suppressExpandOnFocus
an internal variable, remove partial button widget usage in header
Calendar: Fix hover event setting and removing
Datepicker: Improve localization handling, code style
Calendar: Add buttons option
Calendar: Adjust files to match reorganization of external directory
Datepicker tests: Remove pass-through options unit tests

Add Test if these options are set on the underlying calendar instance
Calendar: Use _on for link hover events