Change status caching, fix existing value related methods, introduce
$.date construction with date object, add selected getter

Add calendar widget by copying and renaming datepicker widget files

Add a basic _isValid method for both widgets to check for valid dates.

The method should return the actual date object instead of the copied $.date
object

Add min and max option by extending _isValid method and improving render day
cell mechanism

Simplify calendar generation, use CSS instead of inline styles, fix
destroy method

Simplify calendar generation, remove unneeded inline styles

Fix unit tests after changing HTML structure, remove unneeded tests, adjust
CSS selectors to match new widget structure

Remove shortcut for closing the calendar and erasing the date (CTRL+END)

Use HTML5 date format for reading min and max attributes from input element.
Remove now unneeded helper method for parsing date strings.

Remove duplicated core unit tests from datepicker tests.