use ical as event source

[jens1o]

supersedes #54

fixes #17

[jens1o]

To run this on your local device, you need to have composer (like npm, just for PHP) installed and run composer install in the root directory.

[pascalwittler]

I have nothing against the integration of composer packages or libraries in general, but currently (for over a year) there is not even a reliable workflow for uploading some static files to the web server.

As long as the upload after changes here on Github is achieved by asking people you know and need to reach via chat or personal conversation to copy files by hand, I am against requiring further steps and installed software.

[jens1o]

see #54 (comment)

[soc]

Vor dem Merge bitte noch entweder (mit vernünftiger Commit-Message) squashen, oder merge/fixup-commits loswerden.

[jens1o]

this will (probably) be solved using MediaWiki :)

let's leave this for now