Remove virtual-(less|node)

I much prefer just using npm these days.
Remove Puppet (and Vagrant)

The puppet provisioning of the Vagrant box has been broken for ages due
to floating dependencies. I don't want to support it anymore since
Docker images are almost ready - hence why it goes.
Use CSS source maps

Taking lead from https://github.com/machtfit/django-oscar/commit/22041aab9952aac6683da86cd8c575e905d4252b
Adjust how the "action" param is submitted in order list page

Before this change, the "download as CSV" button wasn't working as there
were two hidden "action" inputs and only the value of the "change order
status" button was being picked up.

This change uses button name attributes to determine which button was
submitted.