Initial 2.0 rewrite

/to @Schoonology 

This is a working version of the 2.0 workspace. It includes the explorer as its own module. I think we should move the explorer to a module "loopback-explorer" that is listed as a dependency of the app and installed by default.

See the tests and the slc pull request of the same name to get a feel for the API. The API will also be available over REST (via loopback).