Bug 1078520 - python client

Implement a python client.  Note to reviewers, there were a couple fairly substantial changes to the way the module in the latest commits.  It's probably best to only really look at the most recent code.
Yeah... but that's only if we extend it... 

And I don't think we're going to change it... If we are it'll probably result in a new signature version... In cases where we want to associated store credentials with a user group or something... but that's way into the future...

Note, new signature version doesn't mean we automatically drop support for the old.