Drop pre-rendered html: MediaEntry.description_html

After a bit of discussion, we decided to drop the
pre-rendered html from the database and render it on
the fly.

In another step, we will use some proper caching method to
cache this stuff.

This commit affects the MediaEntry.description_html part.

mediagoblin/user_pages/views.py

@@ -250,7 +250,7 @@ def atom_feed(request):
 
     for entry in cursor:
         feed.add(entry.get('title'),
-            entry.get('description_html'),
+            entry.description_html,
             id=entry.url_for_self(request.urlgen,qualified=True),
             content_type='html',
             author={