Move out datengartens into their own section

- /datengarten/index.html returns a blog-like list
- /datengarten/index.ics returns a VCALENDAR
- /datengarten/index.xml returns a schedule.xml-style view

No more pretty rendering includes in the content pages,
some more cleanup in the front matter

content/datengarten/37.md

@@ -5,13 +5,14 @@ title: "Datengarten 37"
 no: 37
 subtitle: "Embedded analysis workshop 2011 (Part I)"
 date: 2011-05-12T00:00:00+02:00
-event_date: 2011-05-12T20:00:00+02:00
+event:
+  start: 2011-05-12T20:00:00+02:00
+  end:   2011-05-12T22:00:00+02:00
 location: CCCB
 speaker: cyphunk/Nathan
-language: Englisch
+language: en
 streaming: false
 ---
-{{< datengarten-infobox >}}
 
 based on the tools presented at the 27c3
 ([video](https://www.youtube.com/watch?v=YD7UY0CBvnY),