SourceImage: "user" field support
allow SourceImage to accept filobj/str/bytes as file content
Settings: added get/set methods that accept dotted.path.to.key key paths
removed deprecated setting "deploy-image"
migrated to docker-py>=0.5.0, fixed #56
Merge pull request #57 from nikicat/master

migrated to docker-py>=0.5.0, fixed #56