Allow any postal code by default

Due to the way Madrid handled postal code validations (see issue 533),
by default we were requiring everyone to validate against the local
census *and* to specify valid postal codes.

This could be useful in some cases, but in other cases, the census
validation will be enough and there'll be no need to manually define the
valid postal codes. Besides, some CONSUL installations are used in
organizations or political parties where the postal code validation
doesn't make sense.

app/models/setting.rb

@@ -177,7 +177,7 @@ class Setting < ApplicationRecord
         "machine_learning.comments_summary": false,
         "machine_learning.related_content": false,
         "machine_learning.tags": false,
-        "postal_codes": "00001:99999",
+        "postal_codes": "",
         "remote_census.general.endpoint": "",
         "remote_census.request.method_name": "",
         "remote_census.request.structure": "",

app/models/verification/residence.rb

@@ -104,6 +104,8 @@ class Verification::Residence
     end
 
     def valid_postal_code?
+      return true if Setting["postal_codes"].blank?
+
       Setting["postal_codes"].split(",").any? do |code_or_range|
         if code_or_range.include?(":")
           Range.new(*code_or_range.split(":").map(&:strip)).include?(postal_code&.strip)