Shorten XML for parsed course

Instead of passing the complete XML response to the page, only the part
where the interesting fields for a course are stored should be passed as
a parameter. It also shortens the code in the html.erb file that is
necessary to pull out the wanted fields.

lib/tiss/tiss_crawler.rb

@@ -33,7 +33,7 @@ class TissCrawler
     puts(url)
 
     response = HTTParty.get(url)
-    response.parsed_response
+    response.parsed_response['tuvienna']['course']
   end
 
   def self.get_host