Breaking change.
In the new 2.x project layout, definition of loopback Models is out of
scope of the boot process. The bootstrapper only configures existing
models - attaches them to a dataSource and the app object.
Hide `compile` and `execute` and provide a better API for browserified
applications:
- `boot.compileToBrowserify(options, bundler)` calls `compile` under
the hood and adds all instructions and scripts to the bundler.
- `bootBrowserApp(app)` is exported by loopback-boot when the module
is loaded in a browser, the function loads the instructions as
bundled by `compileToBrowserify`.
This new API hides all implementation details from the user and makes
it easy to add loopback-boot to any build script.