Change environment getJointGroup and getKinematicGroup to return shared pointers

[Levi-Armstrong]

This change improves performance in motion planning. Both the JointGroup and KinematicGroup only have const methods so to avoid making duplicate copies they can all share the same object.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.24%. Comparing base (ad309d7) to head (e11d815).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1092      +/-   ##
==========================================
+ Coverage   89.23%   89.24%   +0.01%     
==========================================
  Files         289      289              
  Lines       16380    16377       -3     
==========================================
- Hits        14616    14615       -1     
+ Misses       1764     1762       -2     

see 1 file with indirect coverage changes