new layout and 3D controls in basic_controls

I've been revising the recent modifications @acornacorn made to 3D controls in interactive_marker_control.cpp in Rviz. Along the way, I made this tutorial easier to use with a 3D cursor device (which I know has not yet been released yet, but I'm working on that.)

I think this pull request supersedes #6.

I will update the tutorial if you agree with these changes.