Datepicker: Introduce value option

Change status caching, fix existing value related methods, introduce
$.date construction with date object, selected property is null by
default, add selected getter
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.
Remove, fix and adjust tests due to split and changed specification.
Remove duplicated demo files and improve some demos. Simplify calendar
generation, use CSS instead of inline styles, fix destroy method,
fix unit tests after changing HTML structure, remove unneeded tests,
adjust CSS selectors to match new widget structure. Make use of
uniqueId method, Fix focus highlighting when month is changed.
Calendar: Add min and max option

Add min and max option by implementing _isValid method and
improving render day ell mechanism.
Calendar: Remove select callback reference
Datepicker: Read min / max attributes
Datepicker: Code clean up for events
Datepicker: remove guard clause to check if element is an input
Datepicker: Remove unwanted keyboard shortcut

Remove shortcut for closing the calendar and erasing the date (CTRL+END)
Datepicker: Make sure calendar sets new option value before datepicker
Datepicker: Make use of _getCreateOptions for min and max options
Datepicker: Simplify usage of calendar options and avoid duplications
Datepicker: Fix input keyboard handling
Datepicker: Update value from input on refresh
Datepicker: Fix dateFormat option setting incl. date-formats demo.
Calendar: Add version property
Datepicker tests: Add common unit tests
Datepicker tests: Add open and close unit tests
Datepicker tests: Remove unneeded disabled / enabled options

Remove unneeded disabled / enabled options as tests exists for disable and
enable methods.
Calendar: Make it possible to set min / max option to null
Datepicker: Improve document click event