Refactor CameraOptic

This MR refactor CameraOptic

• Move and rename it as tomo.newtomo.tomo_detectors.TomoDetectors
• Rework it to be a list of TomoDetector object
• Create an active_detector property

- name: tomo_detectors
  plugin: bliss
  class: TomoDetectors
  package: tomo.newtomo.tomo_detectors
  detectors:
    - $tomo_detector