Add wrapper to get all BodyNodes from a Skeleton

[chhinze]

Before, it was only possible to access multiple BodyNodes by name

---

Before creating a pull request

• Document new methods and classes
• Format new code files using clang-format

Before merging a pull request

• Set version target by selecting a milestone on the right side
• Summarize this change in CHANGELOG.md
• Add unit test(s) for this change

[jslee02]

Looks good to me!

[codecov]

Codecov Report

Merging #1397 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1397   +/-   ##
=======================================
  Coverage   57.27%   57.27%           
=======================================
  Files         366      366           
  Lines       27432    27432           
=======================================
  Hits        15711    15711           
  Misses      11721    11721