Make custom settings editable by the editor in an module

I succeeded to create an custom module with a page where the editor can change settings. What did I exactly do:

1. Created a custom module (docs.kentico.com/display/K82/Creating+custom+modules)
2. Created some custom settings (docs.kentico.com/display/K82/Adding+custom+website+settings)
3. Created a interface (docs.kentico.com/display/K82/Manually+creating+the+interface+for+custom+modules)
4. The code of the webform is:

ASPX:

<%@ Page Language="C#" AutoEventWireup="true" MasterPageFile="~/CMSMasterPages/UI/SimplePage.master" 
    CodeBehind="SiteSettings.aspx.cs" Theme="Default" Inherits="SiteSettings" %>
<%@ Register TagPrefix="cms" TagName="SettingsGroupViewer" Src="~/CMSModules/Settings/Controls/SettingsGroupViewer.ascx" %>
<asp:content contentplaceholderid="plcContent" id="content" runat="server">
    <cms:SettingsGroupViewer ID="SettingsGroupViewer" runat="server" AllowGlobalInfoMessage="false" />
</asp:content>

ASPX.cs

using CMS.Base;
using CMS.ExtendedControls.ActionsConfig;
using CMS.SiteProvider;
using CMS.UIControls;
using System;
using System.Web.UI.WebControls;

public partial class SiteSettings : CMSModalPage
{
    #region "Page events"

    protected void Page_Load(object sender, EventArgs e)
    {
        // Set up header
        CurrentMaster.HeaderActions.AddAction(new SaveAction(this));
        CurrentMaster.HeaderActions.ActionPerformed += HeaderActions_ActionPerformed;

        // Assign category, group and site ID
        SettingsGroupViewer.CategoryName = "BDO.CustomSettings";
        SettingsGroupViewer.SiteID = SiteContext.CurrentSiteID;
    }

    #endregion

    #region "Event Handlers"

    /// <summary>
    /// Handles actions performed on the master header.
    /// </summary>
    /// <param name="sender">Sender object.</param>
    /// <param name="e">Event argument</param>
    protected void HeaderActions_ActionPerformed(object sender, CommandEventArgs e)
    {
        switch (e.CommandName.ToLowerCSafe())
        {
            case "save":
                SettingsGroupViewer.SaveChanges();
                break;
        }
    }
    #endregion
}