Fix locale loading when application boots

In development mode Rails might output some deprecation warnings which
don't appear in test or production. It seems Rails 6 prepares these
warnings ahead of time and they rely on the `#to_sentence` this in turn
loads the locales and but because our gettext based strings are loaded
in an initializer the available locales aren't yet set. Resulting in a
error being raised with our i18n fixes.

This change moves all the gettext and locale setup into a Railtie and
sets everything up in a `before_configuration` block which runs before
any initializers are run.

Fixes:
```
./lib/i18n_fixes.rb:54:in `available_locales': undefined method `map' for nil:NilClass (NoMethodError)
```

config/application.rb

@@ -16,6 +16,7 @@
 # require 'rails/test_unit/railtie'
 
 require File.dirname(__FILE__) + '/../lib/configuration'
+require File.dirname(__FILE__) + '/../lib/alaveteli_localization'
 
 # Require the gems listed in Gemfile, including any gems
 # you've limited to :test, :development, or :production.
@@ -104,12 +105,5 @@ class Application < Rails::Application
     if AlaveteliConfiguration::force_ssl
       config.action_mailer.default_url_options[:protocol] = "https"
     end
-
-    config.after_initialize do
-      AlaveteliLocalization.set_locales(
-        AlaveteliConfiguration.available_locales,
-        AlaveteliConfiguration.default_locale
-      )
-    end
   end
 end

config/initializers/alaveteli.rb

@@ -38,20 +38,17 @@
 require 'core_ext/warning'
 
 require 'use_spans_for_errors.rb'
-require 'i18n_fixes.rb'
 require 'world_foi_websites.rb'
 require 'alaveteli_external_command.rb'
 require 'quiet_opener.rb'
 require 'mail_handler'
 require 'ability'
 require 'normalize_string'
 require 'alaveteli_file_types'
-require 'alaveteli_localization'
 require 'theme'
 require 'xapian_queries'
 require 'date_quarter'
 require 'public_body_csv'
-require 'routing_filters'
 require 'alaveteli_text_masker'
 require 'database_collation'
 require 'alaveteli_geoip'

lib/alaveteli_localization.rb

@@ -1,8 +1,35 @@
-require 'alaveteli_localization/locale'
-require 'alaveteli_localization/hyphenated_locale'
-require 'alaveteli_localization/underscorred_locale'
-
 class AlaveteliLocalization
+  class Railtie < Rails::Railtie
+    config.before_configuration do
+      require 'alaveteli_localization/locale'
+      require 'alaveteli_localization/hyphenated_locale'
+      require 'alaveteli_localization/underscorred_locale'
+
+      require 'routing_filters'
+      require 'i18n_fixes'
+
+      paths = ['locale']
+      paths << 'locale_alaveteli_pro' if AlaveteliConfiguration.
+        enable_alaveteli_pro
+
+      repos = paths.map do |path|
+        FastGettext::TranslationRepository.build('app', path: path, type: :po)
+      end
+      AlaveteliLocalization.set_default_text_domain('app', repos)
+
+      I18n::Backend::Simple.send(:include, I18n::Backend::Fallbacks)
+
+      AlaveteliLocalization.set_default_locale_urls(
+        AlaveteliConfiguration.include_default_locale_in_urls
+      )
+
+      AlaveteliLocalization.set_locales(
+        AlaveteliConfiguration.available_locales,
+        AlaveteliConfiguration.default_locale
+      )
+    end
+  end
+
   class << self
     def set_locales(available_locales, default_locale)
       available, default = parse_locales(available_locales, default_locale)