Rewriting code for notice representation

Getting rid of NoticeListItemAdapter, putting more into ActivityHandlerPlugin
and relying on plugins to handle rendering code of the content. This gives us
a lot more structure and consistency in notice structure and allows activity
plugins to stop rendering certain kinds of notices more easily.

There should also be a property for an ActivityHandlerPlugin class to avoid
rendering notices in the ordinary stream, so we don't have to overload stuff.

plugins/Bookmark/lib/bookmarklistitem.php

@@ -74,7 +74,7 @@ class BookmarkListItem extends NoticeListItemAdapter
 
         $profile = $notice->getProfile();
 
-        $out->elementStart('p', array('class' => 'e-content'));
+        $out->elementStart('div', array('class' => 'e-content'));
 
         // Whether to nofollow
 
@@ -139,6 +139,6 @@ class BookmarkListItem extends NoticeListItemAdapter
                           $nb->description);
         }
 
-        $out->elementEnd('p');
+        $out->elementEnd('div');
     }
 }