A first idea of how BusinessPath will look at the end (after garbage removal...

A first idea of how BusinessPath will look at the end (after garbage removal and refactoring). The ExplanationCache will be a central part of implemenation (and may need some interfaces).

git-svn-id: https://svn.erp5.org/repos/public/erp5/sandbox/amount_generator@35546 20353a03-c40f-0410-a6d1-a30d3c3de9de