Move lxml into setup.py from requirements.txt

As pointed out in issue #2, ``lxml`` is a requirement for this MWS
integration but is not part of ``setup.py`` as a dependency. This fixes
the issue.

Resolves #2.
Update dependencies to release version of Oscar 0.6+

Release versions for Oscar 0.6 and 0.7 are available in PyPI now and can
be referenced properly in ``setup.py``. This removes the dependency to
a specific commit in the ``requirements.txt`` and moves it into
``setup.py`` instead.
Update requirements to latest versions
Fix tests after version upgrades
Set sandbox DB to use atomic DB operations
Remove debug-toolbar from sandbox settings
Add flatpages contrib to installed apps for tests
Fix PEP8 issues
Fix issue with Django 1.5 views requiring 'object_list'
Add build for Django 1.6