[MRG] Appveyor wheelhouse uploader

Here is an update to the appveyor configuration to upload the generated artifacts to a rackspace container. I needed to create the branch in the main sklearn to be able to use traditional sklearn-ci account:

https://ci.appveyor.com/project/sklearn-ci/scikit-learn

I encrypted therackspace secret API key on that AppVeyor account (see the `secure:` prefix).

Once I get a successful build on that branch I will post the link to the resulting containers.

This tool should help use automate the release process for windows build artifacts, in particular by making it easier to test those artifacts prior to a release. The final upload to PyPI when we do a release will still be manual though.