The demo launch files started IMU nodes that were
unused, produced warnings, and created problematic tf trees.
With this commit, they no longer start these nodes.
Quick tests of some of the demos indicate that they
work as well as they did before. However, I did not test
hello_world.launch.

Python 3 was not well supported by ROS Melodic.
stretch_deep_perception required Python 3, which could
cause issues and confusion. To help clarify when code
used Python 3, the filenames had the pattern *_python3.py.

I've changed the filenames to remove this pattern,
since all of the ROS Noetic code will be using Python 3
by default, and ROS Noetic supports Python 3.

+ move up or down to contact handles
+ use new stretch_driver custom effort thresholds
+ successful with tool chest drawer, but has 10 second timeouts after each move until contact