Port "Quickstart in RViz" Tutorial

[sea-bass]

"Quickstart in RViz" Tutorial has been ported to work with ROS2.

The key update to the code is the addition of a ROS2 compatible demo.launch.py and associated RViz configurations (empty and filled out) that also work with ROS2. Previously, this relied on the moveit_resources repository but I have moved these assets within the actual doc/quickstart_in_rviz folder, which has led to a few changes in the CMakeLists.txt.

ros2 launch moveit2_tutorials demo.launch.py rviz_tutorial:=true

The tutorial itself has been updated to correct topic names and sliders that did not originally work by exactly following the ROS1 instructions. Specifically,

• The move_group/monitored_planning_scene topic did not work, but /monitored_planning_scene did.
• The move_group/display_planned_path topic similarly did not work, but /display_planned_path did.
• Replace the MotionPlanning - Slider with Trajectory - Trajectory Slider.
• The RVizVisualToolsGui panel is not available from the Panels drop-down menu -- you actually have to select Add New Panel and look for it from the full list.

Closes Issue #1.

[MarqRazz]

Sorry it took so long to get this reviewed @sea-bass! Thanks for your contributions!