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
Since all changes are saved automatically, it does not make sense to expose it in workspace 3.0.

I am keeping the `saveProject` action around in case we decided to change the loopback-workspace behaviour again.