Add support for MDI list menu item.  

Add support for the RadRibbonBars to have their items merged while in MDI mode.

To reproduce:
- Set the Windows theme to Windows 7 Basic
- Start a RadRibbonForm and maximize it

Workaround:

void Form1_Resize(object sender, System.EventArgs e)
{
    if (this.WindowState == FormWindowState.Maximized)
    {
        this.RibbonBar.RibbonBarElement.IconPrimitive.Padding = new Padding(5, 5, 0, 0);
    }
    else
    {
        this.RibbonBar.RibbonBarElement.IconPrimitive.Padding = Padding.Empty;
    }
}

add additional minimize options:
    - minimize to panel titles
    - minimize to panel buttons

Enable duplication of RadRibbonBar group's element.

When Windows aero effects are enabled and the form width is being decreased, the title bar text appears over the title bar buttons and further more when continuing reducing the width of the form the buttons disappear and a small black rectangle is shown instead.