WebSite title cache should not depend on the web section but on the web_site. This fix the bug that make the WebSite title different from one section to another in case of modification.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@34089 20353a03-c40f-0410-a6d1-a30d3c3de9de