Add content to the Remote Census Configuration tab

- Render remote census configuration content on settings index.
 - Update type method from Setting
   On Admin::SettingsController#index we are using 'all_settings' to
   group all settings by 'type' method.
   'type' method return the first part of key when split by '.'
   To allow use by example: all_settings["remote_census.general"]
   and recover only settings related with this key we have added new
   'elsif' on 'type' method.

spec/models/setting_spec.rb

@@ -53,6 +53,21 @@ describe Setting do
       expect(homepage_setting.type).to eq "homepage"
     end
 
+    it "returns the key prefix for 'remote_census.general' settings" do
+      remote_census_general_setting = Setting.create(key: "remote_census.general.whatever")
+      expect(remote_census_general_setting.type).to eq "remote_census.general"
+    end
+
+    it "returns the key prefix for 'remote_census_request' settings" do
+      remote_census_request_setting = Setting.create(key: "remote_census.request.whatever")
+      expect(remote_census_request_setting.type).to eq "remote_census.request"
+    end
+
+    it "returns the key prefix for 'remote_census_response' settings" do
+      remote_census_response_setting = Setting.create(key: "remote_census.response.whatever")
+      expect(remote_census_response_setting.type).to eq "remote_census.response"
+    end
+
     it "returns 'configuration' for the rest of the settings" do
       configuration_setting = Setting.create(key: "whatever")
       expect(configuration_setting.type).to eq "configuration"