DatePicker improvements

[WesSouza]

Currently, the DatePicker implements a Window that can't be controlled at all (besides exposing a ref, style and shadow).

Ideally, the component should be refactored and split into:

• A calendar: a generic implementation that takes props such as month: number, year: number, selectedDate: string, selectedDateStart: string, selectedDateEnd: string. The name could be CalendarView.
• An input that displays the calendar: following the Select component and the <input type=date> HTML element, a dropdown that shows a masked text input and a button that opens the calendar.

Because Date contains time information, manipulating it can cause the date to shift because of daylight savings times around the world, therefore I suggest falling back to what input=date uses, a date string that is then parsed according to the date strings format.

Optionally:

• A date picker window: using the CalendarView above, the DatePicker could be renamed to DateDialog, and some additional properties should be added to allow icon, title and close button configuration.