display small selects as radio buttons

app/models/champs/drop_down_list_champ.rb

@@ -1,2 +1,3 @@
 class Champs::DropDownListChamp < Champ
+  THRESHOLD_NB_OPTIONS_AS_RADIO = 3
 end

app/models/drop_down_list.rb

@@ -8,6 +8,10 @@ class DropDownList < ApplicationRecord
     result.blank? ? [] : [''] + result
   end
 
+  def enabled_non_empty_options
+    (options - disabled_options).reject(&:empty?)
+  end
+
   def disabled_options
     options.filter { |v| (v =~ /^--.*--$/).present? }
   end