Add Duracloud

Add Duracloud as a Space.

Note this requires #28 and #31 
I don't think this is worthwhile. Unlike ```os.path.join```,  ```urlparse.urljoin``` only accepts two parameters - the base and relative path.  I would have to make almost all the URL with ```+``` before passing it into urljoin, which seems silly at that point.  eg ```urlparse.urljoin('https://' + self.host, 'durastore/' + self.duraspace + '/')```