Refactor accessToken handling into User service

Introduce a new service `LoopBack` that holds accessToken and can
provide other LoopBack-related functionality in the future.
Use lb-ng to generate Model services

Replace 'client/js/services.js' with `client/js/lb-services.js`
generated by `lb-ng`, fix configuration of app depedencies.
Use User.getCurrent() to access current user

Install $http response interceptor to handle 401 errors by redirecting
to `/login`.

Move User.getCurrent to $routeChangeStart handler, so that
the current user data is available to all routes.
Get rid of $rootScope

Replace `$rootScope.nextAfterLogin` with `$location.nextAfterLogin`.

Move `$rootScope.currentUser` to a new service `AppAuth`.
Merge pull request #6 from strongloop/feature/spike-angular-sdk

Use services generated by LoopBack AngularJS SDK