Lidar Safety Node Advanced

[nathanestill]

I changed the code and made it nicer.

[ConnorNovak]

• Function docstring comments
• change "callback" to more specific - e.x. "lidar_cb"
• Not running anything . . .
• In run loop, check for "rospy.is_shutdown"
• Also, throw in a section that waits until it gets lidar data to run main loop. Put in run function.
• Last command in "if name == "main" should be calling run function.
• Set up a rospy.Rate()
• For var name and comments, reference base_link coordinate system
• Draw and save quick diagram labeling geometries
  You're super cool though!

[ConnorNovak]

Please add downward-facing lidar and run some tests.

[ConnorNovak]

1. Output twist messages that conform to the new state controller
2. Register node as safety behavior by following instructions on wiki
3. Implement some way to run with or w/o groundlidar
4. Test with Amy's simulation