Map - slim down Donut marker config panel to a reasonable width

[bobular]

Thanks to #403 the user will see the map and the marker config on first entry. It would be good if we can minimise how much of the map is obscured by the panel.

In the screenshot below we can see that the "Binning method" radio buttons are very wide and do not even need to be there for categoricals.

Tasks and things to consider

• remove Binning method radio buttons for variable types that don't need it (presumably categorical)
• narrow the radio buttons for when they are needed - the default featured variable could be continuous
• Remove the "Donut marker controls" heading? It doesn't save any width but it does save height and is not telling the user anything useful
• Think about long variable names in the variable picker (max width/ellipsis if not already implemented?)
• Think about long value names (in the categorical config table) (ellipsis or wrap?)