DatePicker localisation/format

[rklos]

Use case

My app uses the Polish language. In our language we have different rules for displaying date and time:

• we use day.month.year or, more rarely, year-month-day date format,
• we use leading zeros in out date format,
• we use the 24-hour format (without the AM/PM suffix),
• our week starts on Monday, not Sunday.

It would be nice to be able to customise these things in the DatePicker and TimePicker.

In the graphical version of the DatePicker, I would also like to be able to change the English month and weekday abbreviations to Polish.

Proposal

I would like to achieve something like this using additional API params in DatePicker and TimePicker:

[GroovinChip]

@rklos let's open a separate issue for time picker localization.

[rklos]

Case of the TimePicker moved to #442