Datepicker: Initial commit of widget rewrite work from old branch

History is on the datepicker-dead branch.
Datepicker: Update tests and demos for new structure
Datepicker: Fix the `eachDay` option

Use the `eachDay` option in the other-months demo.
Fix handling of `extraClasses` property, split on space.
Datepicker: Only apply the `ui-state-focus` class name to one cell

This is specifically for multi month pickers. This makes the assumption that
the keyboard is always interacting with the first month in a multi month
calendar. The next step is to store which grid currently has focus and to base
the focus logic off of that.
Datepicker: Clean up tests
Datepicker: Support changing the `appendTo` option after init
Datepicker: Various changes for the `showWeek` option

* Re-add `ui-datepicker-week-col` class name currently used.
* Add test suite.
* Support changing option after initialization.
Datepicker: Support `position` option changes after init
Datepicker: Support changing `eachDay` after initialization
Datepicker: Allow `dateFormat` to be changed after init
Datepicker: Add test to ensure the `<input>`'s value is preselected
Datepicker: Support destroying inline datepickers
Datepicker: Add `value()` and `valueAsDate()` methods
Datepicker: Fix key handling implementation and tests
Datepicker: Use Globalize 1.0.0
Datepicker: Update key handling implementation and tests
Datepicker: Re-adding mouse tests
Datepicker: Add an `isValid()` method
Datepicker: Handle invalid values in `value()` and `valueAsDate()`
Datepicker: Update the picker as the user types valid dates