Merging this before getting back to working on #52

Just a question: since @phracek and @dhodovsk wrote the support for containers -- Nick, would you be interested in having such functionality in fedmod?

fedmod doesn't feel like the right layer for the container parts to me, as I'm seeing it more as a tool for helping with the transition from using metapackages and yum group to using modules.

By contrast, constructing a container from modules feels like part of the regular artifact definition flow:

• individual packages -> module definitions -> artifacts (repositories, container images, OS tree images, AMIs, etc)

For example, I could see "build from module" fitting in better as a build strategy in OSBS than it does as part of a separate CLI tool.

@ttomecek It occurs to me that with fedmod moving to a separate repo, it would also be possible to revert all the recent changes and turn this back into a modtools project for the parts that didn't make their way into fedmod :)