Fix all flake8 issues.
Update to flake8 2.1
Remove threshold and ignored warnings from lint.sh

Also output the errors directly now that it's not over 100 anymore.
Move flake8 configuration to tox.ini

That way it is picked up for example by vim.
Check complexity as well

For now, just add noqa to the functions that fail the complexity test.
Pin requests version

This avoids a pesky UnicodeDecodeError that occurs with Haystack when
trying to rebuild the index.
Merge pull request #1082

Fix a few additional warnings not on original branch

Conflicts:
	oscar/apps/basket/forms.py
	oscar/apps/order/utils.py
	oscar/apps/partner/strategy.py

Fixes #1082