FEATURE: Site settings defaults per locale

This change-set allows setting different defaults for different locales. 

It also:

- Adds extensive testing around site setting validation

- raises deprecation error if site setting has the default property based on env

- relocated site settings for dev and tests in the initializer

- deprecated client_setting in the site setting's loading process

- ensure it raises when a enum site setting being set

- default_locale is promoted to `required` category.

- fixes incorrect default setting and validation

- fixes ensure type check for site settings

- creates a benchmark for site setting

- sets reasonable defaults for Chinese

script/benchmarks/site_setting/profile.rb

@@ -0,0 +1,32 @@
+require 'ruby-prof'
+
+def profile(&blk)
+  result = RubyProf.profile(&blk)
+  printer = RubyProf::GraphHtmlPrinter.new(result)
+  printer.print(STDOUT)
+end
+profile { '' } # loading profiler dependency
+
+require File.expand_path('../../../../config/environment', __FILE__)
+
+# warming up
+SiteSetting.title
+SiteSetting.enable_sso
+SiteSetting.default_locale = SiteSetting.default_locale == 'en' ? 'zh_CN' : 'en'
+SiteSetting.title = SecureRandom.hex
+
+profile do
+  SiteSetting.title
+end
+
+profile do
+  SiteSetting.enable_sso
+end
+
+profile do
+  SiteSetting.default_locale = SiteSetting.default_locale == 'en' ? 'zh_CN' : 'en'
+end
+
+profile do
+  SiteSetting.title = SecureRandom.hex
+end