Use fullcalendar as event display

[niccokunzmann]

Currently, we only provide dhtmlx as output for the calendar.
https://github.com/fullcalendar is an open-source web calendar with many views. We can provide an option to include it. It allows many more views than dhtmlx does.

open-web-calendar/default_specification.json

Line 3 in 68dc26c

"template": "dhtmlx.html",

It is quite easy to create a view for this: https://fullcalendar.io/releases/fullcalendar-scheduler/1.9.4/demos/simple.html

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[niccokunzmann]

Resources to read:

• https://fullcalendar.io/docs/events-json-feed
• https://fullcalendar.io/docs/event-object

Since #27, we have the architecture in place: You can create a fullcalendar strategy to convert the events.

Adding fullcalendar would be good for an events' list.