Created by: detjensrobert
This PR adds a new container build that includes Podman for container-in-container use. Podman does not require a daemon and as such is easier to manage inside an exising container.
The new image builds off the existing onecommons/unfurl image, and follows the existing tagging scheme (latest / stable / TAG), with a -podman suffix (latest-podman / stable-podman / TAG-podman)
Also includes a slimming of the exising image by ~200MB by clearing the pip cache, and typo fixes in the README and an example on using the Docker image.
Resolves onecommons/gitlab-oc#968.