follow yams api change: attributes permissions are now defined for
an 'update' action, no more 'add' / 'delete' which makes no sense in such case.
fix afs.relations_by_section permissions checking of object relation on the way.
Schema of the data
------------------
First take a look at the data schema_ then try to remember that you are browsing
through a heap of data by applying stylesheets to the results of queries. This
site is not a content management system with items placed in folders. It is an
interface to a database which applies a view to retreived data.
.. _schema: schema