Fix/spurious print

The important fix in this PR is in `render_panel.cpp`, where I removed a print that was happening **every time** an interactive marker menu was hidden.

While I was digging around in the code trying to figure out why highlighting doesn't work I also fixed some minor style issues in `interactive_marker_control.cpp`:
* use `static const float` in a cpp file instead of `#define`
* make a function brace consistent with the style in rviz.

Unfortunately highlighting still doesn't work :(