Bugs fixed:
- express helpers like `req.get` are now available in middleware
handlers registered via `app.middleware`
- `req.url` does not include the mountpath prefix now, this is
consistent with the behaviour of `app.use`
The implementation of phased middleware was completely rewritten.
- We no longer use Phase and PhaseList objects from loopback-phase.
- Handler functions are registered via the `Layer` mechanism used by
express router.
- The app keeps the layers sorted according to phases.
84af4194fb