Notable side-effects:
- loopback no longer exports "caller" and "arguments" properties
- kv-memory connector is now properly added to the connector registry
- the file "test/support.js" was finally removed
- `loopback.registry` is now a true global registry
- `app.registry` is unique per app object
- `Model.registry` is set when a Model is created using any registry method
- `loopback.localRegistry` and `loopback({localRegistry: true})` when set to `true` this will create a `Registry` per `Application`. It defaults to `false`.
- Move core models `Model` and `PersistedModel` to `lib/`.
- Move `AccessContext` class to `lib/`, since it is not a model.
- Move all other built-in models to `common/models`.
This is a preparation for extracting model definitions to JSON files.
By splitting the change into multiple commits, git is able to keep track
of file moves (renames).