MP display: add units to joints frame

[v4hn]

I still strictly prefer radian here, but this at least states units explicitly.

Fixes #2263 .

[felixvd]

Good call, should have done this when I had to think about it recently.

This is a human-facing interface and nothing that is copied or written, so degrees are the right choice in my opinion.

[codecov]

Codecov Report

Merging #2264 into master will increase coverage by 0.13%.
The diff coverage is 69.23%.

@@            Coverage Diff             @@
##           master    #2264      +/-   ##
==========================================
+ Coverage   57.77%   57.90%   +0.13%     
==========================================
  Files         326      326              
  Lines       25621    25627       +6     
==========================================
+ Hits        14803    14840      +37     
+ Misses      10818    10787      -31     

Impacted Files	Coverage Δ
...tils/include/moveit/utils/robot_model_test_utils.h	100.00% <ø> (ø)
...os/moveit_servo/include/moveit_servo/servo_calcs.h	100.00% <ø> (ø)
moveit_ros/moveit_servo/src/servo_calcs.cpp	61.48% <20.00%> (+0.12%)	⬆️
.../collision_detection/test_collision_common_panda.h	99.31% <100.00%> (ø)
...it/collision_detection/test_collision_common_pr2.h	100.00% <100.00%> (ø)
moveit_core/utils/src/robot_model_test_utils.cpp	73.07% <100.00%> (ø)
.../ompl_interface/src/detail/constrained_sampler.cpp	46.15% <0.00%> (-17.95%)	⬇️
...e/src/parameterization/model_based_state_space.cpp	72.22% <0.00%> (-2.78%)	⬇️
moveit_core/robot_model/src/joint_model_group.cpp	59.33% <0.00%> (-2.72%)	⬇️
...ics_plugin_loader/src/kinematics_plugin_loader.cpp	60.54% <0.00%> (-2.05%)	⬇️
... and 14 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 589f83a...342729e. Read the comment docs.