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/60.md

@@ -5,14 +5,15 @@ title: "Datengarten 60"
 no: 60
 subtitle: "NinjaPCR"
 date: 2015-11-17T00:00:00+02:00
-event_date: 2015-11-17T20:00:00+02:00
+event:
+  start: 2015-11-17T20:00:00+02:00
+  end:   2015-11-17T22:00:00+02:00
 location: CCCB
 speaker: Shingo Hisakawa
-language: Englisch
+language: en
 streaming: yes
 recording: https://media.ccc.de/v/dg60_NinjaPCR
 ---
-{{< datengarten-infobox >}}
 
 The mass production of DNA amplifiers, which are essential in gene
 testing, has become cheap and stable enough that no longer do we have to