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/38.md

@@ -5,12 +5,13 @@ title: "Datengarten 38"
 no: 38
 subtitle: "Embedded Analysis Workshop (Part II)"
 date: 2011-05-26T00:00:00+02:00
-event_date: 2011-05-26T00:00:00+02:00
+event:
+  start: 2011-05-26T00:00:00+02:00
+  end:   2011-05-26T00:00:00+02:00
 location: CCCB
 speaker: cyphunk/Nathan
-language: Englisch
+language: en
 streaming: false
 ---
-{{< datengarten-infobox >}}
 
 See [Datengarten 37](/post/datengarten_37).