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

spec/models/locale_site_setting_spec.rb

@@ -0,0 +1,21 @@
+require 'spec_helper'
+
+describe LocaleSiteSetting do
+
+  describe 'valid_value?' do
+    it 'returns true for a locale that we have translations for' do
+      expect(LocaleSiteSetting.valid_value?('en')).to eq(true)
+    end
+
+    it 'returns false for a locale that we do not have translations for' do
+      expect(LocaleSiteSetting.valid_value?('swedish-chef')).to eq(false)
+    end
+  end
+
+  describe 'all_values' do
+    it 'returns all the locales that we have translations for' do
+      expect(LocaleSiteSetting.all_values.sort).to eq(Dir.glob( File.join(Rails.root, 'config', 'locales', 'client.*.yml') ).map {|x| x.split('.')[-2]}.sort)
+    end
+  end
+
+end