API v2 - v2 systems_controller and systems index action

- `Api::V2::SystemsController` extends `Api::V2::ApiController` instead
  of `Api::V1::SystemsController` so if a v2 action doesn't work, try
the v1 action for now.
- moved a common method from `SystemsController` to `ApiController`
- fixed some indentations

- [ ] fix broken tests