Use multiple checkerboards

[Naoki-Hiraoka]

Hello. I am Naoki Hiraoka, robot_calibration user.

This pull request is to use multiple checkerboards.

For calibrating a dual-arm robot, we have to capture data with a checkerboard attached to its right arm, and then capture data with another checkerboard attached to its left arm, and then solve the optimization together.
This pull request gives different frame_id to each checkerboard and enables the optimizer to distinguish the frames of the checkerboards.

Multiple checkerboards can be used with modified capture.yaml like below.

features:
  rarm_checkerboard_finder:
    type: robot_calibration/CheckerboardFinder
    topic: /head_camera/depth_registered/points
    camera_sensor_name: camera
    chain_sensor_name: rarm
    frame_id: rarm_checkerboard
  larm_checkerboard_finder:
    type: robot_calibration/CheckerboardFinder
    topic: /head_camera/depth_registered/points
    camera_sensor_name: camera
    chain_sensor_name: larm
    frame_id: larm_checkerboard

[mikeferguson]

Thanks!