In the process of trying to get keyboard_teleop to work,
I encountered a syntax error. It turned out to be due to
"async" being used in an argument and "async" being
a keyword in Python 3. I've replaced "async" with
"return_before_done". This is the main change in this
commit.

These changes make the following code run in ROS Noetic
with Ubuntu 20.04 and Python 3. However, this code has
not been fully tested. The robot moves and appears to
collect data. A fit error appears to be calculated.
The visualization of the fit may have a problem.

+ stretch_calibration collect_check_head_calibration_data.launch
+ stretch_calibration check_head_calibration.sh

For now, I've commented out "class HelloNode" in hello_misc.py
due to a syntax error without an obvious fix.

Detected ArUco markers can now be visualized in rviz.

+ Fixed shebang
+ removed "/" from the start of frame_ids

This simple change makes the following commands behave reasonably:

$ roslaunch stretch_core d435i_low_resolution.launch
$ rosrun rviz rviz

Add missing dependency on realsense (for devel branch)

Add missing dependency on realsense

Checking the calibration now collects fewer higher quality observations.

When checking or performing a new fit, the fit error is checked against a threshold that likely indicates a problem with the calibration.

Code to check the existing calibration. It does the following:

+ Collects a reduced number of new observations with which to check the current calibration.

+ Visualizes and computes the fit of the current calibration to the new observations.

Future work:

+ Improve the reduced number of observations to increase efficiency.

+ Check the numeric results of the fit and provide a warning if the quality is low.

Merge develop into master

added comments & deleted unused code

Merge branch 'bugfix/required_realsense_xacro_arg'

+ Users may define out-of-range goals intentionally if they want to move any joint to its limit without knowing the joint's calibrated limit for a specific robot

+ issue with gripper not opening due to commanded opening aperture violating gripper joint bounds
+ added documentation
+ discards object candidate points based on the height of object and the height of the volume of interest used for perception (height of the robot's camera)
+ appears to correct issue when surface is against a wall, which seemed to result in the wall being detected as a large object on the surface

URDF meshes are now organized per the robot batch ID and copied into place using the update_meshes script