Add standard OSG objects (e.g. Line, Arrows, Text to the viewer. They won't interact with the robot

[petevieira]

No description provided.

[mxgrey]

I propose that these objects live solely in OSG instead of making them DART objects prior to rendering, and we have three different versions of how to add these to the scene:

1. Add directly in the world frame without doing anything special

2. Specify a DART body node which will act like the object's frame (we find the MatrixTransform node that corresponds to that DART body node and add the OSG object as a child of that MatrixTransform)

3. Specify an OSG group node to add it to