Support multiple excludes for enum types

It's not possible to pass it off to search_numeric_attribute directly
since the column "category" does not match the prefix "category_id".

app/logical/concerns/searchable.rb

@@ -329,6 +329,8 @@ module Searchable
       relation = relation.where(name => value)
     elsif params["#{name}_id"].present?
       relation = relation.numeric_attribute_matches(name, params["#{name}_id"])
+    elsif params["#{name}_id_not"].present?
+      relation = relation.where.not(id: relation.numeric_attribute_matches(name, params["#{name}_id_not"]))
     end
 
     relation