renamed default theme to minimal theme in order to clarify the fact that there...

renamed default theme to minimal theme in order to clarify the fact that there is nothing such as a default Web theme in erp5_web

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@25293 20353a03-c40f-0410-a6d1-a30d3c3de9de