PyPI-like functionality to PloneSoftwareCenter

I’ve added some PyPI-like functionality to PloneSoftwareCenter. I’ve sucessfully used the ‘register’ and ’sdist upload’ commands of standard distutils and setuptools respectively to register and upload a release to a local PSC setup.

There’s some TODO items still pending, more when I get back from the beach.

Update: I’ve started a thread on the plone-devel mailing list. Hopefully people will give some input about what they would like to see.