title: Using PySimpleGUI to divide the window in columns gives an error
body: <p>I am tring to construct a GUi that would display two columns:
  one column would have all the input fields and listboxes, the second column would display some data from <code>pandas dataframe</code>.</p>
  
  <p>I thought it would be a good idea to do this using <code>Frames</code>, but I am running into an error when trying to create a <code>Frame</code>:</p>
  
  <pre><code>layout = [sg.Frame('Input data',[[
            sg.Text('Input:'),      
            sg.Input(do_not_clear=False),      
            sg.Button('Read'), sg.Exit(),
            sg.Text('Alternatives:'),
            sg.Listbox(values=('alternatives...', ''), size=(30, 2), key='_LISTBOX_')]])] 
  </code></pre>
  
  <p>Result:</p>
  
  <blockquote>
    <p>TypeError: AddRow() argument after * must be an iterable, not Frame</p>
  </blockquote>
  
  <p>How to fix this?</p>
  
  <p>I am thinking if it is possible to define columns first, using <code>Frame</code>, and then putting the columns into the definition of <code>layout</code>?</p>