Rework the implementation to use loopback-workspace 3.0

Requires strongloop/loopback-workspace#56.

My intention is to fix the `TODOs` in subsequent pull requests, most of them require non-trivial changes in loopback-workspace.

/to @ritch please review
This is a short-lived item, I'll implement it in next few days.

I do follow the convention in other comments.