title: I can't make Gtk Picture Widget currect size
body: <p>[the picture widget fills a strange space][1]
  [1]: https://i.stack.imgur.com/Hktgz.png</p>
  <p>I've set both halign and valign for every widget to Gtk.Align.START, but while the label widget works okay, the picture widget still fills the window until there is no enough space.</p>
  <p>So I put a frame out of the picture, but nothing changes.</p>
  <p>What's wrong with it?</p>