Add collision objects to scene from RViz

[v4hn]

It would be useful to add collision objects to the planning scene through the RViz panel.
The "Scene Objects" tab already allows to move and scale objects (no flexible resize though...).

Adding objects, especially resizable cubes and cylinders from this GUI would make setting up a planning scene a much more interactive experience instead of changing parameters in some file and loading it over and over again.

[felixvd]

Strongly agree, this would be a great contribution.

[jrgnicho]

I'm currently addressing this

[rhaschke]

Fixed via #2198.