Port rqt controller manager to ROS 2

[ijnek]

This is a port of rqt_controller_manager from ROS 1 to ROS 2.

• rqt_controller_manager package
  • A port of rqt_controller_manager from ROS1, but with some modifications listed below that were necessary due to fundamental changes in the ros2 control architecture.
  • states of the controllers have changed
    • not loaded
    • unconfigured
    • inactive
    • active
    • finalized
  • the controller namespace has been replaced with controller node name
  • parameters are obtained directly from controller manager using get_parameter service rather than accessing parameter server
  • relpaces manual service calls (configure_controller, load_controller, etc.) with helper methods from controller_manager_services

ps.
The ROS1 version uses BSD. This port has modified it to Apache 2.0 because that was the only way I could get the tests passing, and it seems like everything else has been changed to apache 2.0 during hte ROS2 port.

[ijnek]

Closing, and reopening PR against upstream.