FEATURE: Allow plugins to easily add defaults to GlobalSetting

usage:

GlobalSetting.add_default("plugin_setting_name", "value")

app/models/global_setting.rb

@@ -137,6 +137,14 @@ class GlobalSetting
       end
   end
 
+  def self.add_default(name, default)
+    unless self.respond_to? name
+      define_singleton_method(name) do
+        default
+      end
+    end
+  end
+
   class BaseProvider
     def self.coerce(setting)
       return setting == "true" if setting == "true" || setting == "false"

spec/models/global_setting_spec.rb

@@ -50,6 +50,20 @@ describe GlobalSetting do
     end
   end
 
+  describe '.add_default' do
+    after do
+      class <<GlobalSetting; remove_method :foo_bar_foo; end
+    end
+
+    it "can correctly add defaults" do
+      GlobalSetting.add_default "foo_bar_foo", 1
+      expect(GlobalSetting.foo_bar_foo).to eq(1)
+
+      GlobalSetting.add_default "cdn_url", "a"
+      expect(GlobalSetting.foo_bar_foo).not_to eq("a")
+    end
+  end
+
   describe '.redis_config' do
     describe 'when slave config is not present' do
       it "should not set any connector" do