Added support for Disabling Days/Date Ranges

Added support for disabling specific days or date ranges.

This can be done by passing the optional parameters “disableDays” or
“disableDateRange” (or both if needed) to datetimepicker. Both
parameters expect arrays.

For disableDays, you can specify a day name (e.g. “Monday”) to disable
all Mondays. Alternatively, you can specify a date in the format
(“YYYY/mm/dd”) to disable that particular date.

For disableDateRange, pass the start date and end date in an array.
Start and End dates are inclusive.