Treeportlet: Implement deferred tree rendering.

When having a large repository-tree with more than 2000 objects,
the three portlet slows down every site reload. To avoid this performance issue
we render the the tree deferred.
Merge pull request #250 from 4teamwork/pg_deferred_treeportlet

Treeportlet: Implement deferred tree rendering.
Passing search string from live search to advanced search.
Using SearchableText from the url as default value in advanced search.
Removed unnecessary super call in advancedsearch.