Use DockerParser from updated spython 0.0.73

[stain]

This fixes #3

btw, it seems to time out, so manifest = json.loads(response['message'])[0] is not executed in ContainerRecipe/extract.py - just moved it into the if block to avoid errors.

[vsoch]

So sorry that I didn't see this! I'm literally going down emails from top to bottom, and this was toward the bottom. Take a look at #5 and we can add some of the nice changes you've done here that aren't present there after review.