lb: update the usage of workspace and juggler API

Use `model.properties.create()` to add properties to a model (this was a breaking change in loopback-workspace 2.5.0 - strongloop/loopback-workspace#47). 

Use `err.details.context` and `err.details.codes` when printing ValidationError (there was a breaking change in loopback-datasource-juggler a long time ago).

/to @ritch or @sam-github please review