Use Ember-Orbit and Orbit.js instead of Ember Data

Client changes:
- Data sources: Memory and JSON API are connected with api find method assisting memory find
- Non authenticated routes use slug for URLs, admin (edit) routes use ids

Server changes:
- API uses links for JSON API compliance, see http://jsonapi.org
- Server uses content type "application/json-patch+json", see: http://tools.ietf.org/html/rfc6902
- API route for GET /posts/[:id[,id...]|:slug] supports id, slug or comma separated ids