Fix field alignment in order admin.
Merge
Move permission checks for retreiving an order into OrderManager.get_for_user and make the order email re-send require a form post.
pep8 + Python 3 fix for address field pairing in admin.
Handle the APPEND_SLASH setting

This is done in mezzanine entirely
pep8 fix
Restore urlpattern for order email resend.
Handle cart changes invalidating existing discount codes. Closes #168.
Fix import