Add WorldInteractiveMarkerViewer.

[brianhou]

This subclasses aikido::rviz::InteractiveMarkerViewer to create a viewer for a dart::simulation::World. This would automatically update the viewer as skeletons are added to the World, which is a first step toward using them properly in all of our demo scripts.

@psigen mentioned that dart::simulation::World has some additional overhead if we aren't doing things with dynamics. I'm using World for now for lack of something better in DART, but we should seriously think about a better longer-term solution.

Other issues:

• There doesn't seem to be a mutex associated with Worlds, so there might be some thread-safety issues here?
• Cloning a World doesn't replicate the transforms or the joint states. This line in DART suggests that this is still a TODO...

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[codecov]

Codecov Report

Merging #242 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #242   +/-   ##
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  Coverage   70.92%   70.92%           
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  Files         173      173           
  Lines        5118     5118           
  Branches      809      809           
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  Hits         3630     3630           
  Misses       1000     1000           
  Partials      488      488

[brianhou]

When I'm using this new viewer class in the (poorly-named) block_stacking demo, I sometimes get this error when I exit the script:

*** Error in `./devel/bin/block_stacking': corrupted double-linked list: 0x0000000000660e40 ***

This StackOverflow answer suggests that heap overflow might be to blame, but I'm not sure where this could be happening. If anyone sees something that could be causing that issue, please let me know!