content: Fix imported posts (markdown syntax, article types)

The auto-importer has created several issues with the markdown syntax which
needed manual fixing. Additionally quite a lot of event annoucements were
categorized as article.

content/blog/2007/2007-01-04-freifunktreffen-am-040106/index.md

@@ -1,7 +1,7 @@
 ---
 authors:
 - desc
-categories: article
+categories: event
 draft: false
 lastmod: '2007-01-04T00:10:28+01:00'
 publishDate: '2007-01-04T00:10:28+01:00'
@@ -19,4 +19,3 @@ treffen sich die Freifunker vom LOK am Donnerstag den 04.01.2006 ab
   Ausbreitung
 
 Es sind natuerlich wieder alle eingeladen.
-