Python3 support

I worked on porting django-oscar to Python3.

It has been quite some work.
I needed to adapt a couple of dependencies (django-dynamic-fixture in particular doesn't support well python3) or use the git version so I'm not sure this could be used out of the box by this time.

At this point, put appart the CSV test all the tests are passing under python 3.3 and python 2.7:

Ran 774 tests in 53.552 seconds
OK (1 skipped)

I'd really like to discuss about the apps.dashboard.reports.csv_utils since I'm not really sure I understand its goals.

If you are interested I could group changes and open several incremental pull requests in order to add this to the code base incrementally.