Rename start_position to initial_position due to ros2_control change

* Change fake driver

* Add velocity state interfaces

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'