Displays docker container's name

This PR is trying to fix #9

- Add a struct called ContainerRef, which contains container name and its aliases.
- ``ListContainers()`` returns a slice of ``info.ContainerRef``.
- Display docker container's alias in the sub container list.

We probably need more changes in the UI. We may need more PRs to fix #9.
Question: This is accessed as object.ContainerRef?