Support for request argument to suit_row_attributes

This patch improves upon the new feature in 0.2.1 where list rows could be styled based on the object instance (http://django-suit.readthedocs.org/en/develop/list_attributes.html) by supporting a request argument to suit_row_attributes. This makes it possible to vary the styling based on i.e. the authenticated user (say, highlight new items).

Docs and tests are updated.