Calendar field or two calendar fields with Dependence

This widget allows you to add a calendar field in the form.
Here, the pop-up calendar box are used alone as a calendar or optional two calendars are added, which are interdependent.
Usage example for arrival and departure, where the departure date must be > = than date of arrival.

In a dependency first two calendar fields must be created. After that first calendar must have as "Calendar Dependent" the other calendar.