Added Date Zoom feature at Planning Box. The Planning Box was partially refactored
in some parts by me (and also Romain) these lasts months, this commit was the initial 
one.

The tests and documentation update will come soon.



git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@15881 20353a03-c40f-0410-a6d1-a30d3c3de9de