Bump several dependencies for Python 3 compatibility

Debug toolbar 1.2 has some more usable panels, and less trouble with
jQuery interactions. It also is the first version to be compatible with
Django 1.7, which we'll support in the upcoming Oscar release.

django-compressor 1.4 has finally been released and supports Python 3
and comes with lots of other goodies.

sorl-thumbnail seems to be barely maintained anymore. I don't dare
switch to the beta version for Python 2. There's a few critical issues
reported on their issue tracker atm:
https://github.com/mariocesar/sorl-thumbnail/issues?labels=critical&page=1&state=open

django-nose-querycount is not Python 3 compatible and has been moved.
Test against newest Django versions

Django 1.5.8 and Django 1.6.5 have since been released.
Replace compat.urlparse with six.moves.urlparse.parse

six is presumably better tested than our own code. Plus it allows us
using both urlencode and urlparse.
More concise pattern to exclude external DeprecationWarnings in tests

I was seeing a lot of DeprecationWarnings. As all we really care about
is DeprecationWarnings in Oscar, a more blanket statement should be
sufficient.
Python 3 fix for filter()

I presume filter returns an iterator in Python 3.
Fixes for reverse_lazy and Python 3

Django has some issues with reverse_lazy, e.g.
https://code.djangoproject.com/ticket/19378

This made me review where we use it, and change it to reverse where it's
unneeded.

One method also triggered the same error message as above. Luckily the
entire method is unnecessary, as FormView already does the correct
thing.