title: wx.adv.CalendarCtrl in wxPython does not work with sizers
body: <p>I would need add calendar to my small utility. I have a hello world code like this:</p>
  <pre><code>import wx
  import wx.stc as stc
  import wx.adv as adv
  
  class MyFrame(wx.Frame):
      def __init__(self):
          super().__init__(parent=None, title='My fancy form app with calendar')
          panel = wx.Panel(self)
          my_sizer = wx.BoxSizer(wx.VERTICAL)
          self.SetMinSize(wx.Size(400,450))
  
          # Headline Text
          self.headline_text = wx.StaticText(panel, style = wx.TE_CENTER &amp; ~wx.TE_LEFT &amp; ~wx.TE_RIGHT, label=&quot;This text will be placed to the top of my form&quot;)
          my_sizer.Add(self.headline_text, 0, wx.ALL | wx.EXPAND, 5)
  
          # Calendar under the text
          self.cal = adv.CalendarCtrl(self, 10, wx.DateTime.Now())
          my_sizer.Add(self.cal, 0, wx.ALL | wx.CENTER, 5)
  
  
  if __name__ == '__main__':
      app = wx.App()
      frame = MyFrame()
      app.MainLoop()
  </code></pre>
  <p>Without the block of code with Calendar, this works well. BoxSizer can arrange buttons, text labels, tables etc. - But the calendar kills the sizer and everything is in the top left corner.</p>
  <p>So please, what is the proper usage of CalendarCtrl object? Thanks!</p>