Select the current grouping option in a list

This layout requires less screen space, it reduces
the amount of information displayed at all times.

I replaced the list of radio buttons with a select list
and updated the code to detect a change of value accordingly.
Use shorter labels for the group selection

Long labels get cut due to the fixed width of the menu.
Use a consistent layout for both fieldsets
Remove fixed text "Visualization: " from heading
Merge branch 'layout'