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

lib/site_settings/validations.rb

@@ -0,0 +1,66 @@
+module SiteSettings; end
+
+module SiteSettings::Validations
+  def validate_error(key)
+    raise Discourse::InvalidParameters.new(I18n.t("errors.site_settings.#{key}"))
+  end
+
+  def validate_min_username_length(new_val)
+    validate_error :min_username_length_range if new_val > SiteSetting.max_username_length
+    validate_error :min_username_length_exists if User.where('length(username) < ?', new_val).exists?
+  end
+
+  def validate_max_username_length(new_val)
+    validate_error :min_username_length_range if new_val < SiteSetting.min_username_length
+    validate_error :max_username_length_exists if User.where('length(username) > ?', new_val).exists?
+  end
+
+  def validate_default_categories(new_val, default_categories_selected)
+    validate_error :default_categories_already_selected if (new_val.split("|").to_set & default_categories_selected).size > 0
+  end
+
+  def validate_default_categories_watching(new_val)
+    default_categories_selected = [
+      SiteSetting.default_categories_tracking.split("|"),
+      SiteSetting.default_categories_muted.split("|"),
+      SiteSetting.default_categories_watching_first_post.split("|")
+    ].flatten.to_set
+
+    validate_default_categories(new_val, default_categories_selected)
+  end
+
+  def validate_default_categories_tracking(new_val)
+    default_categories_selected = [
+      SiteSetting.default_categories_watching.split("|"),
+      SiteSetting.default_categories_muted.split("|"),
+      SiteSetting.default_categories_watching_first_post.split("|")
+    ].flatten.to_set
+
+    validate_default_categories(new_val, default_categories_selected)
+  end
+
+  def validate_default_categories_muted(new_val)
+    default_categories_selected = [
+      SiteSetting.default_categories_watching.split("|"),
+      SiteSetting.default_categories_tracking.split("|"),
+      SiteSetting.default_categories_watching_first_post.split("|")
+    ].flatten.to_set
+
+    validate_default_categories(new_val, default_categories_selected)
+  end
+
+  def validate_default_categories_watching_first_post(new_val)
+    default_categories_selected = [
+      SiteSetting.default_categories_watching.split("|"),
+      SiteSetting.default_categories_tracking.split("|"),
+      SiteSetting.default_categories_muted.split("|")
+    ].flatten.to_set
+
+    validate_default_categories(new_val, default_categories_selected)
+  end
+
+  def validate_enable_s3_uploads(new_val)
+    validate_error :s3_upload_bucket_is_required if new_val == "t" && SiteSetting.s3_upload_bucket.blank?
+  end
+
+end