Add support for enum site settings that render as a dropdown; use a dropdown for default_locale

app/models/locale_site_setting.rb

@@ -0,0 +1,21 @@
+class LocaleSiteSetting
+
+  def self.valid_value?(val)
+    supported_locales.include?(val)
+  end
+
+  def self.all_values
+    supported_locales
+  end
+
+
+  private
+
+  @lock = Mutex.new
+
+  def self.supported_locales
+    @lock.synchronize do
+      @supported_locales ||= Dir.glob( File.join(Rails.root, 'config', 'locales', 'client.*.yml') ).map {|x| x.split('.')[-2]}
+    end
+  end
+end

app/models/site_setting.rb

@@ -203,7 +203,7 @@ class SiteSetting < ActiveRecord::Base
   setting(:title_fancy_entities, true)
 
   # The default locale for the site
-  setting(:default_locale, 'en')
+  setting(:default_locale, 'en', enum: 'LocaleSiteSetting')
 
   client_setting(:educate_until_posts, 2)