This is the first step of refactoing ListBox.

There are still a lot to do, such as removing makeTreeBody,
replacing the HTML rendering with Page Template,
performance tuning, etc. But this version is already cleaner
and less buggy than the original.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@7837 20353a03-c40f-0410-a6d1-a30d3c3de9de