[Pas2js] Calendar/scheduler support

[Michael Van Canneyt]

Hello,

I've added a unit for calendar (scheduler) support to pas2js SVN.

It's an import unit of the fullcalendar.js open source calendar:
https://fullcalendar.io/

A small demo can be seen here:

https://www.freepascal.org/~michael/fullcalendar/demofullcalendar.html

This is one of the most complete calendars I've found, and it can now be
used in Pas2js. I'm using it in a production environment, so I'm pretty
confident it works :)

Comments, requests for improvements: all welcome.

Enjoy!

Michael.