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/88.md

@@ -8,13 +8,14 @@ subtitle: "Progress in the Embedded GPU space"
 speaker: Robert Foss
 speaker_url: https://twitter.com/memcpy_io
 date: 2018-05-08T00:00:00+02:00
-event_date: 2018-05-08T20:00:00+02:00
+event:
+  start: 2018-05-08T20:00:00+02:00
+  end:   2018-05-08T22:00:00+02:00
 location: CCCB
-language: Englisch
+language: en
 streaming: true
 recording: https://media.ccc.de/v/dg-88
 ---
-{{< datengarten-infobox >}}
 
 Ten years ago no one would have expected the embedded GPU ecosystem in Linux to be what it is now. Today, a large number of GPUs have Open Source support and for those that aren't supported yet, improvements are happening at a rapid pace.