Updated kuksa-client autocompletion

[argerus]

An update to the way autocompletion works in kuksa-client. Builds on top of the newly added support for kuksa.val.v1 by @rafaeling.

• Instead of listing the complete path for all completions, list only the currently completable path components.
• Only use columnar completion style.
• Complete branches with a trailing '.' and leafs without.

[rafaeling]

Looks good to me, I think https://github.com/eclipse/kuksa.val/pull/650 can be closed.