Update datepicker.js

Adding numbersCharachters: ["0","1","2","3","4","5","6","7","8","9"], option to define digits of Persian/Arabic numbers. For usage just set numbersCharachters: ["۰","۱","۲","۳","۴","۵","۶","۷","۸","۹"], then the display numbers would be in Persian/Arabic.

This is actually forked from 1.11.2.