Engine: API v2 - wrapping single-object responses and ping controller

WORK IN PROGRESS (comments welcome, i think...?)

- [x] wrapped single-object responses with a root-node
- [ ] wrapped collection responses with a root-node
- [ ] collection response metadata
- [ ] make single-object response root-node optional
- [ ] read http param for root-node name
- [x] ping action
- [ ] other ping controller actions